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The Lancet: Obesity linked to premature death, with greatest effect in men
A study of 3.9 million adults published today in The Lancet finds that being overweight or obese is associated with an increased risk of premature death. The risks of coronary heart disease, stroke, respiratory disease and cancer are all increased. Overall, the excess risk of premature death (before age 70) among those who are overweight or obese is about three times as great in men as in women.
WHO estimates that 1.3 billion adults worldwide are overweight, and that a further 600 million are obese. The prevalence of adult obesity is 20% in Europe and 31% in North America. WHO uses body-mass index (BMI, in kg/m2), which relates weight to height, and defines BMI 18.5-25 as normal, 25-30 as overweight, 30-35 as moderately obese, and over 40 as severely obese.
For example, for height 1.6m (5’3”) overweight is about 60-80 kg (140-170 lb; 10-12 stone), and for height 1.8m (5’11”) overweight is about 80-100 kg (180-210 pounds; 13-15 stone). Normal BMI spans a range of similar length below this; moderate obesity spans a range of similar length above.
“On average, overweight people lose about one year of life expectancy, and moderately obese people lose about three years of life expectancy” says Dr. Emanuele Di Angelantonio from the University of Cambridge, Cambridge, UK, the lead author. “We also found that men who were obese were at much higher risk of premature death than obese women. This is consistent with previous observations that obese men have greater insulin resistance, liver fat levels, and diabetes risk than women.” [1]
The study found an increased risk of premature death for people who were underweight, as well as for people classed as overweight. The risk increased steadily and steeply as BMI increased. A similar trend was seen in many parts of the world (figure 1) and for all four main causes of death (figure 4).
Where the risk of death before age 70 would be 19% and 11% for men and women with a normal BMI [2], the study found that it would be 29.5% and 14.6% for moderately obese men and women (BMI 30-35). This corresponds to an absolute increase of 10.5% for men, and 3.6% for women – three times as big (Appendix p. 45). The authors defined premature deaths as those at ages 35-69 years.
The new study brings together information on the causes of any deaths in 3.9 million adults from 189 previous studies in Europe, North America and elsewhere. At entry to the study all were aged between 20 and 90 years old, and were non-smokers who were not known to have any chronic disease when their BMI was recorded. The analysis is of those who then survived at least another five years. Of 3951455 participants (69% women, Appendix p. 22), 385879 died.
The study also estimated the population-attributable fraction for mortality due to overweight and obesity (PAF) – ie, the reduction in deaths in a population that would occur if a risk factor were eliminated. The authors say that assuming that the associations between high BMI and mortality are largely causal, if those who were overweight or obese had WHO-defined normal levels of BMI, then the proportion of premature deaths that would be avoided would be about one in 7 in Europe and one in 5 in North America.
“Obesity is second only to smoking as a cause of premature death in Europe and North America,” says co-author Professor Sir Richard Peto, University of Oxford, Oxford, UK. “Smoking causes about a quarter of all premature deaths in Europe and in North America, and smokers can halve their risk of premature death by stopping. But, overweight and obesity now cause about 1 in 7 of all premature deaths in Europe and 1 in 5 of all premature deaths in North America.” [1]
The researchers also broke down the normal BMI range and found a slightly increased risk at the lower end of it (at 18.5-20 kg/m2).
The authors note that one important limitation is that their only measure of obesity was BMI, which does not assess fat distribution in different parts of the body, muscle mass, or obesity-related metabolic factors such as blood sugar or cholesterol.
Writing in a linked Comment, Dr David Berrigan, Dr Richard Troiano and Dr Barry Graubard from the National Cancer Institute, National Institutes of Health, Bethesda, MD, USA, discuss the methodological limitations of global studies measuring BMI and mortality and the need for improved study designs, as well as the challenges that remain in the effort to translate epidemiological evidence of excess body weight and mortality into effective guidelines and public health interventions. They say: “Challenges in deriving global public health recommendations are unlikely to be resolved by ever larger datasets without further developments in study data and design.”
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Professor Nikolai Petrovsky is the Director of the Department of Diabetes and Endocrinology at Flinders Medical Centre
It is intuitive that if obesity is highly associated with increased risk of type 2 diabetes, hypertension, and hyperlipidaemia, all in themselves major risk factors of premature cardiovascular disease, that obesity sine qua non should be associated with increased mortality risk, as shown by this analysis.
What was not intuitive was previous studies claiming mild obesity was not associated with excess mortality, almost certainly a flawed finding due to a failure to correct for confounders in the analysed datasets.
As a diabetologist, the question is not whether obesity is associated with excess mortality, which it clearly is, but what do we do about it as a society?
Dr Myles Young is a postdoctoral researcher in the School of Education at the University of Newcastle, Australia
Obesity in men is one of the greatest public health challenges facing Australia. Currently, 70% of Australian men are currently overweight/obese compared to 56% of women. Men are also more likely than women to be obese in every age group. In the past 30 years, the average BMI of Australian men has increased twice as fast as the international average.
While obesity impacts men and women, the Lancet paper has indicated that men generally suffer greater obesity-related health consequences compared to women, even when their body mass index is the same. This is partially due to sex differences in body fat distribution. Men are more likely than women to store fat around their waist, which is a risk factor for type 2 diabetes and heart disease.
Despite the increased risks, men are far less likely than women to consider themselves as overweight, see their weight a health problem, attempt weight loss. As a result, men are greatly under-represented in research. This makes it difficult to provide men with evidence-based weight loss advice. Men report they prefer programs that are convenient and time efficient. Also, while research shows that men prefer a male-only approach, very few studies have recruited men only (~5%). Many programs also contain dietary restrictions and exercise prescription that men consider unacceptable and unsustainable.
At our research centre, we have developed and tested a range of male-only weight loss programs which specifically address men’s preferences and values (e.g., frank and realistic approach, use of humour, focus on scientific basis of recommendations, encouragement of autonomy). A major hook of our studies is that we teach men how to lose weight without giving up beer! The programs have assisted men to achieve clinically meaningful improvements in weight and many other health indicators including blood pressure, physical activity, quality of life, alcohol risk, portion size and sexual function.
Lauren Ball is Professor of Community Health and Wellbeing at The University of Queensland.
The Lancet article clearly highlights that overweight and obesity is a major risk factor for morbidity and mortality. Given the substantial and increasing prevalence of obesity across the world, additional strategies are required to support patients to have healthy lifestyle behaviours, including eating well and exercising regularly.
This article also comes at a time where we cannot ignore the role of lifestyle behaviours on our health. Governments need to place much higher priority on supporting healthy lifestyles, including changes to health care system structures, regulating food supply and incentivising physical activity opportunities.
We need to take innovative action if we are to have an innovative outcome, and this cannot be ignored any more.
Associate Professor Marina Reeves is a National Breast Cancer Foundation Research Fellow at The University of Queensland
There had been a need for this type of analysis due to the confusion around the ‘obesity paradox’. Some previous research had suggested that being overweight was actually better, or protective, particularly for older adults. This study removes of a lot of the ‘noise’ in previous research by excluding smokers and those with pre-existing disease.
These results show the importance of advocating for funding for preventative health services and how to manage the large proportion of Australians who are already overweight or obese and in need of assistance to manage their weight.
Dr Lennert Veerman, is from the School of Public Health at The University of Queensland. He recently published on how a sugar tax would impact on Australian health outcomes
In this landmark study, the authors have shown that overweight is associated with increased mortality. By restricting the analysis to disease-free never-smokers who were followed up for at least five years, they removed much – but not all - of the bias that plagued earlier studies. The study proves that overweight is not good for health, even at an advanced age.
This confirms that the majority of Australians risk an early grave due to their weight. Diets alone are not going to fix this, and blaming individuals is stigmatizing and achieves nothing. We need to reduce waist lines across the board, and governments have to take the lead.
Healthy food needs to be available and affordable, and a junk food levy would discourage unhealthy consumption, and bring in funds to subsidize healthy food. Australia needs fruits, veggies and wholemeal bread, not sugared drinks.
Active transport – walking, cycling, public transport - has to be made easier so car use can be reduced. Australia needs footpaths and bikeways, not extra car lanes.
Professor Sanchia Aranda is CEO, Cancer Council Australia
This study is consistent with what we also know about the relationship between obesity and cancer. Given the unprecedented population weight gain in Australia over the last 30 years, we can expect to see the number of cancers and cancer deaths related to obesity and overweight increase in the future unless we take action.
Cancer Council estimates show around 4000 cancers diagnosed in Australia each year are related to obesity or overweight alone. Even more cancer cases are linked to poor nutrition and inadequate physical activity.
Women are more likely to be diagnosed with a weight-related cancer. Around 2300 of the 4000 obesity-related cancer cases diagnosed annually are in females. This is partly because of the high level of association between body mass and cancers of the female breast and the endometrium. Obesity is also a major risk factor for cancers of the oesophagus, colon and kidney, in both men and women.
Unless we improve our diets and our level of physical activity, we will see incidence of obesity and overweight-related cancers continue to increase. Cancer is already Australia’s biggest cause of premature death. Obesity is a major challenge for governments, federal, state and local, which must take some responsibility for how food is formulated, marketed and labelled and how communities can be supported in being more active. It is also important for individuals to be more aware that their weight can have a significant impact on their cancer risk.
Professor Rachel Huxley is from the Curtin University Faculty of Health Sciences
The worldwide prevalence of obesity is high and increasing. Partly because the prevalence of obesity differs by region, for all-cause mortality there was wide variation across regions with North America at the top, followed by Europe, Australia/New Zealand and East Asia.
These findings suggest that if the entire population had ideal levels of BMI this would avoid about 1 in 5 premature deaths in North America, 1 in 7 in Europe, 1 in 10 in Australia/New Zealand, and 1 in 20 in East Asia, assuming that the associations of overweight and obesity with mortality in our primary analyses largely reflect causal effects.
In addition, the results showed a substantially higher mortality rate not only among those in WHO’s underweight category, but also in those with BMI of 18.5 - 20 kg/m2, suggesting that in excessively lean populations being underweight remains a cause for concern.
Most previous analyses have focused on people living in one particular country or continent, even though relationships of overweight and underweight might differ from one population to another.
We showed that wherever overweight and obesity are common the relationship with all-cause mortality is positive and broadly similar, supporting strategies to combat the entire spectrum of excessive adiposity worldwide.
Professor Anna Peeters is Professor of Epidemiology and Equity in Public Health at the World Health Organization Collaborating Centre for Obesity Prevention at Deakin University
This is an important study using the largest sample so far of healthy never smokers from around the world to demonstrate the high risks of mortality for those with obesity.
It demonstrates that for Australia and New Zealand there is an increase in the risk of dying of around one third for every increase in BMI unit after the overweight range.
With two-thirds of Australian adults overweight or obese this underscores the seriousness of current obesity rates for future life expectancy in Australia. Obesity may lead to the first decrease in life expectancy seen in decades.
Equally important is the demonstration of the impact of overweight and obesity on premature mortality. The study estimates that if we are able to prevent overweight and obesity in Australia we would prevent 1 in 6 premature deaths.
If we needed yet another reason to step up our efforts to prevent obesity, this is it. We must see comprehensive obesity prevention policies from our government, including restrictions on unhealthy food and drink marketing, a sugary drinks tax and a national physical activity and nutrition strategy.
Tim Olds is a professor in the School of Health Sciences at the University of South Australia.
Interesting study. One weakness is the exclusion of about 60% of participants for various reasons, including the rather odd exclusion of people who have ever smoked. In other studies, this has been shown to shift the BMI associated with the lowest mortality (longest life expectancy) towards the lower end of the spectrum. In other words, if the study included people who had ever smoked, the "ideal" BMI would likely be higher. Eclusion of those who have ever smoked might bias the sample towards higher socio-economic status participants, and people with generally healthier habits.
The study does cast some light on, and brings into question, the so-called "obesity paradox" — the finding that overweight people live longer. You see this even in these data in the Australasian and South Asian subsets.
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