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Health News from NHS Choices

Constantly updated health news across a range of subjects.

NHS Choices News

  • Holidays and parties mean we may drink more than we think

    "The amount of alcohol people in England drink has been underestimated by the equivalent of 12 million bottles of wine a week," BBC News reports.

    It has long been known there is a big gap between the amount people say they drink in national surveys, like the Health Survey for England, and the amount of alcohol known to be sold in England.

    In this new survey researchers set out on the assumption that while people may accurately report their standard drinking patterns from week to week, they may forget the drinking they do on special occasions, such as bank holidays, parties, weddings, wakes or big sporting events (which, for many England fans, is akin to a wake).

    The study used a large phone interview to estimate the amount of extra drinking going on during these types of occasions. They found this accounted for an extra 12 million bottles of wine a week in England – just under a staggering eight and a half million litres, which is more than enough to fill three Olympic-size swimming pools.

    The results seem plausible. As the scientists point out: "The impact of atypical and special occasion drinking is reflected in evening presentations to emergency units, which peak on weekends but also sports events, bank holidays, and even commemorative occasions such as Halloween."

    If you are concerned about whether you may be drinking more than you should, you can download the Change4Life Drinks Tracker app, which is available for iOS and Android devices.

    Where did the story come from?

    The study was carried out by UK researchers from Cardiff University, Bangor University, Liverpool John Moores University, and the London School of Hygiene and Tropical Medicine. It was funded by Alcohol Research UK.
     
    The study was published in the peer-reviewed medical journal BioMed Central. This is an open-access journal, so the study is free to read online or download as a PDF.

    The UK media reported the story accurately.  

    What kind of research was this?

    This was a cross-sectional survey aiming to provide a more accurate picture of how much alcohol people in England drink.

    The researchers say there is a big gap between the amount people report drinking in national surveys and the amount of alcohol being sold in England. So are we a nation of liars in denial about our drinking habits?

    Rather than fibbing, the researchers suspected people might be being asked the wrong type of questions on alcohol surveys. You are usually asked what your average alcohol consumption is, say, over a week. People might not think to include special events in this estimate, such as drinking at a wedding or a birthday party, because they are not typical.

    The scientists designed a large telephone interview study to see whether the special occasion drinking might make up the shortfall between estimates of typical drinking and alcohol sales. 

    What did the research involve?

    The team conducted a large-scale telephone survey between May 2013 and April 2014 of people aged 16 years or over living in England.

    Respondents (n = 6,085) provided information on typical drinking (amounts per day, drinking frequency) and changes in consumption associated with routine atypical days (e.g. Friday nights) and special drinking periods (e.g. holidays) and events (e.g. weddings).

    The team acknowledged it did not collect a representative sample of alcohol consumers and abstainers on a national basis, but instead used national population estimates and stratified drinking survey data to weight responses to match the English population.

    The analysis looked to identify additional alcohol consumption associated with atypical or special occasion drinking by age, sex and typical drinking level. 

    What were the basic results?

    Accounting for atypical and special occasion drinking added more than 120 million units of alcohol per week (equivalent to 12 million bottles of wine) to population alcohol consumption in England.

    The greatest impact was seen among 25- to 34-year-olds with the highest typical consumption, where atypical or special occasions added approximately 18 units a week (144g) for both sexes.

    Those reporting the lowest typical consumption (≤1 unit/week) showed large relative increases in consumption (209.3%) with most drinking associated with special occasions.

    In some demographics, adjusting for special occasions resulted in overall reductions in annual consumption – for example, women aged 65 to 74 years in the highest typical drinking category.

    The Health Survey for England, a nationally representative survey, estimates alcohol consumption only accounted for 63.2% of sales. The new survey, including the special occasion drinking, accounted for 78.5%. 

    How did the researchers interpret the results?

    The research team concluded: "Typical drinking alone can be a poor proxy for actual alcohol consumption. Accounting for atypical/special occasion drinking fills 41.6% of the gap between surveyed consumption and national sales in England."

    From a public health perspective they said: "These additional units are inevitably linked to increases in lifetime risk of alcohol-related disease and injury, particularly as special occasions often constitute heavy drinking episodes.

    "Better population measures of celebratory, festival and holiday drinking are required in national surveys in order to adequately measure both alcohol consumption and the health harms associated with special occasion drinking." 

    Conclusion

    This large telephone survey sought to generate a more accurate estimate of England's alcohol consumption by taking account of atypical drinking days like Friday nights, holidays and events such as weddings.

    It found atypical and special occasion drinking added more than 120 million units of alcohol a week (about 12 million bottles of wine) to population alcohol consumption in England

    This accounted for some of the discrepancy between self-reported alcohol consumption and alcohol sales, but not all. The Health Survey for England, a nationally representative survey, estimates alcohol consumption only accounts for 63.2% of sales. The new survey improved this to 78.5%.

    This begs the question, where is the other 21.5% going? There are many potential explanations for this. One is that people are pretty bad at estimating how much they drink, and generally underestimate it, for whatever reason, when asked.

    An alternative, rather worrying, explanation is that a significant portion could be consumed by under-16s, who were excluded from the survey. And there could be people who just can't help downplaying the amount they drink, whether consciously or unconsciously, even to strangers on the telephone.

    The research team highlighted a number of limitations of its own research. First, the survey did not attempt to generate a representative sample of alcohol consumers and abstainers on a national basis.

    The scientists say their survey acts as a proof of concept, and a larger nationally representative survey is needed to test the usefulness of this methodology as a national alcohol monitoring tool. For example, participation rates were quite low (just 23.3% of those contacted) and the sample had more women, older people and people of white ethnicity than is true for England as a whole.

    The estimates also might be imprecise. For example, the team didn't know if special drinking events were instead of or as well as the normal drinking days. In their analysis, they opted for a conservative measure by removing an average drinking day's consumption for each special event day reported.

    The results make sense. As the scientists point out: "The impact of atypical and special occasion drinking is reflected in evening presentations to emergency units, which peak on weekends but also sports events, bank holidays, and even commemorative occasions such as Halloween."

    If you find yourself regularly drinking more than the recommended daily limits (3-4 units for men, 2-3 units for women), you may have an alcohol misuse problem that may require treatment

    Links To The Headlines

    English drink 12 million bottles of wine a week more than estimated. BBC News, May 22 2015

    Forgotten holidays and lost birthdays leave English drinking underestimated. The Guardian, May 22 2015

    Drinkers in England consuming 12 million more bottles of wine a week than previously thought. The Independent, May 22 2015

    English alcohol consumption 'hugely' underestimated, research suggests. The Daily Telegraph, May 22 2015

    Links To Science

    Bellis MA, Hughes K, Jones L, et al. Holidays, celebrations, and commiserations: measuring drinking during feasting and fasting to improve national and individual estimates of alcohol consumption. BMC Medicine. Published online May 22 2015



  • Quarter of sun-exposed skin samples had DNA mutations

    A sobering BBC News headline greets sun worshippers on the eve of the spring bank holiday: "More than a quarter of a middle-aged person's skin may have already made the first steps towards cancer."

    Sunlight is made up of ultraviolet (UV) radiation. Low levels of exposure to UV light are actually beneficial to health – sunlight helps our bodies produce vitamin D.

    But prolonged exposure can change (mutate) the DNA in the cells. Over time the mutations accumulate, turning the skin cells cancerous, which can lead to either non-melanoma or melanoma skin cancer.

    As part of a study into skin cancer, researchers analysed skin removed from the eyelids of four people aged 55 to 73 known to have a varying history of sun exposure (but not a history of cancer) to see what DNA mutations had built up.

    To their surprise they found hundreds of normal cells showing DNA mutations linked to cancer, called "mutant clones", in every 1sq cm (0.1 sq in) of skin, and there were thousands of DNA mutations per cell.

    The results were based on skin cells from the eyelids of just four people, so we don't yet know if the same would be found in other skin areas, or in other people, or what proportion of the mutated cells would eventually progress to skin cancer. 

    Where did the story come from?

    The study was carried out by researchers from The Wellcome Trust Sanger Institute in the UK, and was funded by The Wellcome Trust and the Medical Research Council.

    It was published in the peer-reviewed journal, Science.

    The BBC and the Daily Mail reported the story accurately and reiterated the best ways to lower your risk of getting skin cancer. 

    What kind of research was this?

    This was a genetics study looking at changes in the DNA of normal skin cells to see what proportions were linked to cancer.

    Skin cancer is one of the most common forms of cancer. There are two main types of skin cancer:

    • non-melanoma skin cancer – where cancer slowly develops in the upper layers of the skin; there are more than 100,000 new cases of non-melanoma skin cancer every year in the UK
    • melanoma skin cancer – a more serious type of skin cancer; there are around 13,000 new cases of melanoma diagnosed each year in the UK and 2,000 deaths

    Radiation from too much sun exposure causes damage to the DNA of skin cells. When certain combinations of mutations accumulate, the cell can become cancerous, multiplying and growing uncontrollably. 

    Scientists know about lots of skin cancer mutations, but these tend to have been studied using samples of cancerous skin cells. Researchers don't know what combination of mutations is needed to transform healthy skin cells into cancer, or in what order.

    Approaching the problem from a different direction, this team looked at healthy skin cells to see what mutations might be accumulating in a pre-cancerous stage. 

    What did the research involve?

    The scientists analysed the DNA of healthy eyelid skins cells removed from four people during plastic surgery (blepharoplasty). They looked for DNA mutations they knew were linked to cancer later on. The removed eyelid skin was reported to be normal and free of any obvious damage.

    The team used eyelid skin because of its relatively high levels of sun exposure and because it is one of the few body sites to have normal skin removed.

    They say this procedure is performed for age-related loss of elasticity of the underlying skin, which can cause eyelid drooping sometimes severe enough to disrupt vision, although the epidermis remains otherwise normal.

    The skin sample donors were three women and one man, aged 55 to 73. Two had low sun exposure, one moderate and one high. Three were of western European origin and one was of south Asian origin. It was not clear how sun exposure was assessed.  

    What were the basic results?

    The researchers found a lot more cancer-related mutations in the normal cells than they were expecting. In all, their analysis pinpointed 3,760 mutations. The pattern of DNA mutations "closely matched" those expected for UV light exposure and that seen in skin cancers. 

    DNA is made up of a code of letters known as base pairs. The team estimated people have around two to six mutations per million base pairs per skin cell. This, they said, was lower than the number of mutations usually found in skin cancer, but higher than found in other solid tumours.

    Overall, they estimated around 25% of all skin cells carried a certain type of cancer-linked mutation called NOTCH mutations. While not enough to cause cancer on their own, if other mutations accumulate on top of the NOTCH mutations, they may cause cancer in the future. 

    How did the researchers interpret the results?

    Dr Peter Campbell, head of cancer genetics at Sanger, told the BBC News website: "The most surprising thing is just the scale; that a quarter to a third of cells had these cancerous mutations is way higher than we'd expect, but these cells are functioning normally."

    He added: "It certainly changes my sun worshipping, but I don't think we should be terrified … It drives home the message that these mutations accumulate throughout life, and the best prevention is a lifetime of attention to the damage from sun exposure." 

    Conclusion

    This study estimated around 25% of normal skin cells have DNA mutations that could prime them to develop into skin cancer in the future. This was a lot higher than the scientists expected.

    The genetic analysis of the study was robust, but used skin samples from just four people. This severely limits the generalisablity of the findings to the general population. For example, the results might be different for people of different ages, sun exposures and skin colours, so we don't know if this is true for most people.

    Similarly, the researchers only used eyelid cells. There may be something unique about eyelid tissue that is linked to this higher than expected mutation rate. This may or may not be true for skin from other areas. At the moment, we don't know if the one in four estimate applies to other skin areas.

    The good news is there are simple and effective ways of reducing your risk of skin cancer. The best way to prevent all types of skin cancer is to avoid overexposure to the sun and to keep an eye out for new or changing moles.

    A few minutes in the sun can help maintain healthy levels of vitamin D, which is essential for healthy bones, but it's important to avoid getting sunburn. Wearing protective clothing such as sun hats, seeking shade, and wearing sun cream of at least SPF 30 are all advised.

    Read more about how to enjoy the benefits of the sun without exposing your skin to damage

    Links To The Headlines

    Quarter of skin cells 'on road to cancer'. BBC News, May 22 2015

    Skin cancer alert for the over-50s: Millions failing to heed advice over sun damage. Daily Mail, May 22 2015

    Links To Science

    Martincorena I, Roshan A, Gerstung M, et al. High burden and pervasive positive selection of somatic mutations in normal human skin. Science. Published online May 22 2015



  • Minor ailment scheme doesn't provide free Calpol for all

    "Thousands discover Calpol has been free on NHS 'for years' as mum's Facebook post goes viral," the Daily Mirror reports.

    This and other similar headlines were prompted by a post made on the social networking site Facebook. In the post, it was claimed that all medicines for children were available for free on the NHS as part of the minor ailment scheme.

    "I was in Boots yesterday buying Calpol and happened to complain to the cashier how expensive it is. She told me, to my amazement, that if you register your details with them under the minor ailments scheme that all medicines for children are free – a scheme that has been going for eight years."

    The post went viral, being "shared" and "liked" more than 100,000 times in the space of a few days.

    But there are a number of inaccuracies both in the Facebook post and in the media's reporting of the story. 

    What is the minor ailment scheme?

    The minor ailment scheme is designed to enable people with minor health conditions to access medicines and advice they would otherwise visit their doctor for.

    It allows patients to see a qualified health professional at a convenient and accessible location within their community, and means patients do not need to wait for a GP appointment or queue up for a valuable A&E slot with a non-urgent condition.

    Childhood ailments that may be treated under the scheme include:

    If the patient being treated is exempt from paying prescription charges – because they're under 16 or over 60, for example, or they have a prescription prepayment certificate (PPC) – you don't have to pay for the medicine. 

    Important points about the minor ailment scheme

    There are a number of important points that have not been made clear by the media:

    • The minor ailment scheme is not a national scheme. It is not possible to say exactly which medical conditions are covered because this will vary depending on the location and the particular service.
    • The scheme is designed to offer medication to meet an acute need. It is not an opportunity for parents to stock up on free children's medications – if a pharmacist thinks someone is trying to abuse the system, they can refuse any request for treatment at their discretion.
    • The pharmacist has no obligation to provide branded medication such as Calpol. If there is a cheaper generic version available that is known to be equally effective, it is likely that will be provided instead.
    • Claims that the scheme is secretive are incorrect. Information about the minor ailment scheme has been freely available on the NHS Choices website since 2008.

    Read more about the services offered by pharmacies and how they can often save you a trip to the GP.

    Links To The Headlines

    Thousands discover Calpol has been free on NHS 'for years' as mum's Facebook post goes viral. Daily Mirror, May 20 2015

    No need to cough up for Calpol - it's FREE on the NHS: Thousands discover they're entitled to various medications after mother's Facebook post goes viral. Daily Mail, May 20 2015

    Calpol for FREE: Hundreds find they're entitled to free medication after mum's social post. Daily Express, May 20 2015

    Did you know you can get Calpol for free? Metro, May 20 2015



  • Is paracetamol use in pregnancy harmful for male babies?

    "Paracetamol use in pregnancy may harm male foetus," The Guardian reports. Researchers found evidence that taking paracetamol for seven days may lower the amount of testosterone testicular tissue can produce – using human foetal testicular tissue grafted into mice.

    Low testosterone levels in male pregnancies have been linked to a range of conditions, ranging from the relatively benign, such as undescended testicles, to more serious conditions, such as infertility and testicular cancer.

    Reassuringly, just taking a one-day course of paracetamol did not affect the level of testosterone. It seems any effect could be from continuous daily use only, rather than occasional use, which is how most people would probably take paracetamol.

    An obvious caveat is that as the series of experiments was performed in mice, it is not known what the effect would be in humans. It is also not known whether the effect of regular daily use would be reversible and over what timescale. And we also don't know whether exposure in pregnancy would actually have any detrimental effects in a male child.

    Paracetamol is generally believed to be safe in pregnancy, but – as with all medicines – pregnant women should only take them if absolutely necessary in the lowest effective dose and for the shortest period of time.  

    Where did the story come from?

    The study was carried out by researchers from the University of Edinburgh, the Edinburgh Royal Hospital for Sick Children, and the University Department of Growth and Reproduction in Copenhagen.

    It was funded by The Wellcome Trust, the British Society of Paediatric Endocrinology and Diabetes, and the UK Medical Research Council.

    The study was published in the peer-reviewed journal, Science Translational Medicine.

    In general, the media reported the story accurately, though many of the headline writers decided to discuss the "harms" of paracetamol – such as The Guardian's headline, "Paracetamol use in pregnancy may harm male foetus" – which is an unhelpful term.

    Apart from the fact this study involved mice, not men, there is no evidence a temporary drop in testosterone levels would cause permanent harm to a male foetus. The effect could well be temporary and reversible.

    The Daily Mail went particularly over the top with its claim that, "the popular painkiller is believed to have lifelong effects on baby boys, raising their risk of everything from infertility to cancer". The Mail may think this is the case, but most qualified experts would question this due to lack of evidence. 

    What kind of research was this?

    This was a laboratory study using a mouse model to look at the effect of paracetamol on testicular development. Testes produce the sex hormone testosterone.

    Previous research found an association between low sex hormone exposure in the womb and reproductive disorders, such as undescended testes at birth, or low sperm count and testicular cancer in young adulthood.

    The researchers wanted to investigate whether exposure to paracetamol reduces the level of testosterone production. As it would be unethical to study this in pregnant women, the researchers used a mouse model.

    Paracetamol is one of the drugs believed to be safe to use in pregnancy. This safety is based on observational studies of use during human pregnancy, as randomised controlled trials – the gold standard in research – are not performed in pregnancy for ethical reasons.   

    What did the research involve?

    The researchers grafted samples of human foetal testicular tissue into mice. In a series of laboratory experiments, they gave the mice different doses of oral paracetamol over the course of a week. The researchers measured what effect the paracetamol had on the level of testosterone produced by the testicular tissue.

    Human foetal testes were obtained from pregnancies terminated in the second trimester. Small 1mm3 tissue samples of these testes were grafted under the skin of mice so the researchers could see what effect paracetamol had on their growth in an animal that has some similarities to humans.

    The mice had their testicles removed so their production of testosterone would not influence the study. Their immune system was also dampened down to reduce the chances of rejecting the testicular tissue.

    After a week – enough time for the testicular tissue to establish a blood supply – the mice were given injections of a hormone called human chorionic gonadotrophin (hCG), which stimulates testosterone production and is usually present in the womb. The mice were then randomly assigned to be given different strengths and regimes of oral paracetamol or placebo.

    The researchers measured the level of testosterone at different time points during the study. They also measured the weight of the seminal vesicle, a gland that holds the liquid that mixes with sperm to form semen. Previous research has shown the growth of seminal vesicles is sensitive to sex hormones.

    Experiments were also performed on the mice to measure the effect of paracetamol on their production of testosterone. 

    What were the basic results?

    Testosterone levels were reduced by exposure to paracetamol for seven days. A dose of 20mg/kg three times a day for seven days, the equivalent of a normal dose in adults, resulted in:

    • 45% reduction in testosterone production by the testicular tissue grafts
    • 18% reduction in seminal vesicle weight

    Exposure to 20mg/kg three times in one day was tested under the premise that most pregnant women would only use paracetamol for a short period of time. This did not reduce testosterone levels or cause any change in seminal vesicle weight.

    High-dose paracetamol of 350mg/kg once a day for seven days did not change the level of testosterone, but it did result in reduced seminal vesicle weight in host mice of 27%.

    Graft survival was 65% over the two-week experiment period. There was no difference in graft weight between mice exposed to any dose of paracetamol and placebo. The mice appeared healthy and had no change in body weight. 

    How did the researchers interpret the results?

    The authors concluded that: "One week of exposure to a human-equivalent therapeutic regimen of acetaminophen [paracetamol] results in reduced testosterone production by xenografted human foetal testis tissue, whereas short-term (one day) use does not result in any long-lasting suppression of testosterone production."

    They say that because the study was performed in mice, it cannot directly inform new recommendations for the use of paracetamol in pregnancy, but suggest pregnant women should consider limiting their use of the drug. 

    Conclusion

    This was a well-designed laboratory study looking at the effect of paracetamol on testicular development. As it would be unethical to study this in pregnant women, the researchers used a mouse model. This involved grafting samples of human foetal testicular tissue under the skin of mice.

    The main finding from the study was that oral paracetamol reduced testosterone production if given at a dose equivalent to humans, three times a day for one week. A single dose of paracetamol did not reduce testosterone production.

    As the researchers say, they tested the effect of single dose exposure as it is assumed that pregnant women are more likely to use paracetamol occasionally rather than continuously. 

    The study's strengths include the randomisation procedure, which meant different doses and regimes of paracetamol could be directly compared with the control condition.

    However, this study has some limitations because of the nature of a mouse model. These include:

    • graft testicular tissue may not respond in exactly the same way as normal testicular development in the womb
    • the grafts were fragments of testis tissue – an intact testicle may act differently
    • the mice were immunocompromised, which may have influenced the results

    The results of this study suggest that regular paracetamol for seven days may reduce the production of testosterone by the developing testicle. However, further studies would be required to determine if this would be the case in humans.

    It is also not clear whether the effect would be reversible and over what timescale. It is further completely unknown whether pregnancy exposure would actually have any detrimental effects in the male child – for example, in terms of the development of sexual characteristics at puberty, or upon future fertility.

    At present, the product safety information for paracetamol does not preclude its use in pregnancy. Paracetamol is the painkiller of choice during pregnancy, as alternatives such as ibuprofen, and particularly aspirin, are thought to be associated with a higher risk of complications.

    Paracetamol is also excreted in breast milk, but this is not believed to be in an amount that would harm the baby. Infant versions of paracetamol such as Calpol, however, are not licensed in babies under the age of two months.

    As with all medicines, pregnant women should only take them if absolutely necessary, in the lowest effective dose and for the shortest period of time. If you have a painful condition that persists for more than one to two days, ask your midwife or the doctor in charge of your care for advice.

    Links To The Headlines

    Paracetamol use in pregnancy may harm male foetus, study shows. The Guardian, May 20 2015

    Paracetamol during pregnancy may affect male babies, study shows. The Independent, May 21 2015

    Taking paracetamol while pregnant 'could harm baby boys': Drug raises risk of conditions such as infertility and cancer later in life. Daily Mail, May 20 2015

    Pregnant women warned paracetamol may harm unborn sons' fertility. ITV News, May 20 2015

    Limit paracetamol in pregnancy, say scientists. BBC News, May 20 2015

    Links To Science

    van den Driesche S, Macdonald J, Anderson RA, et al. Prolonged exposure to acetaminophen reduces testosterone production by the human fetal testis in a xenograft model. Science Translational Medicine. Published online May 20 2015



  • Mildly cold weather 'more deadly' than heatwaves or very cold snaps

    "Mildly cold, drizzly days far deadlier than extreme temperatures," The Independent reports. An international study looking at weather-related deaths estimated that moderate cold killed far more people than extremely hot or cold temperatures.

    Researchers gathered data on 74,225,200 deaths from 384 locations, including 10 in the UK. The results showed that the days most countries have the fewest deaths linked to temperature are those with warmer temperatures than average.

    Therefore, the researchers calculate, the majority of "excess deaths" occur on days that are colder than average. Because extreme temperatures occur on only a few days a year, they have an impact on fewer deaths than the majority of moderately cold days.

    Overall, the researchers say, 7.71% of all deaths can be attributed to temperature based on their statistical modelling.

    One hypothesis offered by the researchers is that exposure to mild cold may increase cardiovascular stress while also suppressing the immune system, making people more vulnerable to potentially fatal conditions.

    The researchers suggest that their findings show public health officials should spend less time planning for heatwaves, and more time thinking about how to combat the effect of year-round lower than optimum temperatures.  

    Where did the story come from?

    The study was carried out by researchers from 15 universities and institutes in 12 countries led by a team from the London School of Hygiene and Tropical Medicine.

    It was funded by the UK Medical Research Council. The study was published in the peer-reviewed medical journal The Lancet and has been made available on an open-access basis, so it is free to read online or download as a PDF.

    The media reports focused on the finding that moderately cold weather – such as that experienced in the UK for much of the year – caused more deaths than hot weather or extremely cold weather. The Daily Telegraph gave a good overall summary of the research.

    The Independent's claim that "mildly cold, drizzly days" are "far deadlier than extreme temperatures" is an extrapolation, as the study didn't look at drizzle or rain as a risk factor, just temperature.

    The Guardian includes a number of reactions from independent experts, such as Sir David Spiegelhalter's, presumably tongue-in-cheek, suggestion that "perhaps they are really saying that the UK climate is killing people". 

    What kind of research was this?

    This study was a meta-analysis of data on temperatures and deaths around the world to find out what effect temperature has on the risk of death, and whether people are more likely to die during cold weather or hot weather.

    The researchers used statistical modelling to estimate the proportions of deaths in the regions studied that could be attributed to heat, cold, and extreme heat and cold. This type of study can tell us about links between variables such as temperature and death rates, but not whether one causes the other. 

    What did the research involve?

    Researchers collected data on temperature and mortality (74,225,200 deaths) from 384 locations in 13 different countries, during time periods from 1985 to 2012. They used statistical analysis to calculate the relative risk of death at different temperatures for each location.

    The countries included were Australia, Brazil, Canada, China, Italy, Japan, South Korea, Spain, Sweden, Taiwan, Thailand, the UK and the US. About one-third of the locations sampled were in the US.

    The researchers were not able to adjust figures to take account of the potential effects of other factors, such as income levels in the different countries, although they used air pollution data when it was available.

    The researchers divided the temperature data from each location into evenly spaced percentiles, from cold to hot days. This was so the temperatures for the coldest days would be in the lowest percentiles of 1 or 2, while the highest temperatures would be at the top range, 98 or 99.

    They defined extreme cold for a location as below the 2.5th percentile, and extreme heat as above the 97.5th percentile. They looked for the "optimum" temperature for each location, being the temperature at which fewest deaths attributable to temperature were recorded.

    They calculated the deaths linked to temperatures above or below the optimum, and sub-divided that again to show deaths linked to extreme cold or heat.

    The statistical analysis used a complex new model developed by the researchers, which allowed them to take account of the different time lag of different temperatures.

    The effects of very high temperatures on death rates are usually quite shortlived, while very cold temperatures may have an effect on deaths for up to four weeks. 

    What were the basic results?

    Across all countries, colder weather was linked to more excess deaths than warmer weather – approximately 20 times as many (7.29% deaths in colder weather compared with 0.42% in warmer weather). 

    For all countries, the optimum temperature – when there were fewest deaths linked to weather – was warmer than the average temperature for that location.

    In the UK, for example, the average temperature recorded was 10.4C, while optimum temperature ranged from 15.9C in the north east to 19.5C in London. The optimum temperature for the UK was in the 90th centile, meaning that 9 out of 10 days in the UK are likely to be colder than the optimum.

    The proportion of all deaths linked to extremely hot or cold days was much lower than that linked to less extreme hot or cold. The researchers say extreme heat or cold was responsible for 0.86% of deaths according to their statistical modelling (95% confidence interval 0.84 to 0.87).

    However, the relative risk of dying at extremes of temperatures was increased, with a sharp increase in deaths at the hottest temperatures for most countries.  

    How did the researchers interpret the results?

    The researchers say their results have "important implications" for public health planning, because planning tends to focus on how to deal with heatwaves, whereas their study shows that below-optimal temperatures have a bigger effect on the number of people who die.

    They say deaths from cold weather may be attributed to stress on the cardiovascular system, leading to more heart attacks and strokes. Cold may also affect the immune response, increasing the chances of respiratory disease.

    They say their results show that public health planning should be "extended and refocused" to take account of the effect of the whole range of temperature fluctuation, not just extreme heat. 

    Conclusion

    Many of the headlines focus on the finding that moderate cold may be responsible for more deaths than extreme hot or cold weather.

    Perhaps more interesting is the finding that the optimum temperature for humans seems to be well above the temperatures we usually experience, especially in colder countries like the UK. If this is true, then the finding that most deaths occur on days colder than the optimum is unsurprising, as most days are colder than the optimum temperature.

    The relative unimportance of very hot or very cold days in terms of mortality is interesting, because most research and public health planning has focused on extreme weather. However, this depends partly on the definition of extreme temperature.

    The researchers used 2.5 upper and lower percentiles to decide on what was extreme for a particular location, so by definition these temperatures are experienced on very few days. Even though the relative risk of death is increased on those days, the absolute number of deaths is nowhere near as high as on the majority of days.

    That doesn't mean it's not worth planning for the increased risk of deaths during extreme temperatures. In London, for example, the relative risk of death is more than doubled on days with temperatures below 0C, compared with days at the optimum temperature of 19.5C.

    Read more advice about coping with heatwaves as well as very cold snaps.

    There are some limitations to the study we should be aware of. First, although it sampled data from 13 countries from very different climates, it didn't include any countries in Africa or the Middle East. This means we can't be sure the findings would apply worldwide.

    Second, the study did not take into account some confounders that could affect how many deaths occur in warmer or colder periods – for example, levels of air pollution, whether people have access to shelter and heating, the age make-up of a population, and whether people have access to nutritious food all year round.

    This also makes it difficult to know how governments or public health bodies can make plans using this new data, as we don't know whether the effects of moderate cold on mortality could be affected by public health measures.

    In the UK, the NHS already plans for more hospital admissions during the winter months, taking account of factors such as the amount of flu-like illness circulating in the population, as well as the temperature.

    Read more advice about winter health.

    Links To The Headlines

    Mildly cold, drizzly days far deadlier than extreme temperatures for Brits, says study. The Independent, May 21 2015

    Moderately cold weather 'more deadly than heatwaves or extreme cold'. The Guardian, May 21 2015

    Cold weather twenty times more deadly than hot weather, study suggests. The Daily Telegraph, May 21 2015

    Links To Science

    Gasparrini A, Guo Y, Hashizume M, et al. Mortality risk attributable to high and low ambient temperature: a multicountry observational study. The Lancet. Published online May 20 2015