But how much obesity causes these conditions has been relatively unknown and unexplored. Now, a study published in October 2019 in PLoS Genetics is shining light on the toll of obesity, along with how extra weight may affect men and women differently. “We found that obesity is involved in two-thirds of the leading causes of death, meaning that we as a society need to become better at preventing obesity,” says Jenny Censin, MD, researcher at Nuffield Department of Medicine at the University of Oxford in England, and first author of the study. Using a scientific model that enabled them to determine a causal relationship between obesity and additional health outcomes, Dr. Censin’s team found that in women extra weight increased the risk for type 2 diabetes more than in men. Meanwhile, in men extra weight elevated the risk for chronic kidney disease and chronic obstructive pulmonary disease (COPD) more than in women. “These findings indicate that the effects of obesity differ between men and women, which is something we need to learn more about so that we can optimize disease prevention for both men and women,” she says. Obesity is a growing health crisis, both in the United States and around the world. According to the World Health Organization (WHO), worldwide obesity has nearly tripled since 1975; in the United States, the CDC’s National Health and Nutrition Examination Survey (NHANES) estimates that 39.6 percent of adults are obese. RELATED: Obesity Rate Now Tops 40 Percent in the United States, Data Show
How Obesity Is Associated With Chronic Disease and Early Death
A wealth of research, including a past prospective study that followed more than 1 million adults over 14 years, shows a strong association between obesity and the risk of death from all causes. For example, a panel of experts commissioned by the Obesity Society in 2012 reviewed all the existing evidence on obesity and health risks. In an article published in the journal Obesity, they concluded that obesity is a disease that causes functional impairment and reduced quality of life, serious disease, and more early deaths. Yet determining the degree to which factors such as obesity, high cholesterol, smoking, or high blood pressure cause a condition or early death is tricky. “It can be difficult to establish the causes of any disease, because other factors can muddy the water and lead us to the wrong conclusions,” says Censin. Clarifying the causes of disease is critical because it enables doctors to focus on the right thing when it comes to disease prevention, she says. “One way to be more certain that something truly causes a disease is to use an approach called Mendelian randomization, a method that uses genes that individuals carry naturally in order to tease out the causes of disease,” says Censin. RELATED: How Obesity and Heart Disease Are Connected
What Is Mendelian Randomization?
Mendelian randomization is named after the scientist Gregor Mendel, who is considered the founder of the science of genetics. This method uses genetic variants to determine whether an observational association between a risk factor and an outcome signals a true cause-and-effect relationship, according to the JAMA Guide to Statistics and Methods. At birth, some people may or may not inherit a genetic variant that affects their risk for a certain health marker — for example, a genetic variant that raises LDL or “bad” cholesterol. Investigators can follow the health outcomes between those individuals who have the specific variant and those who do not, and the difference in outcome is attributed to the variant. “In this study, we examined whether people that carry excess weight (or obesity) are at higher risk of different diseases. Looking at hundreds of thousands of people, we examined hundreds of naturally occurring genetic variants that each increase the risk of obesity by a very small amount,” says Censin. “The approach we used allowed us to make reliable insights into the extent by which obesity causes disease, and to compare how this differs between women and men,” she says.
Obesity Is Associated With Major Causes of Death
To determine the risks of obesity and how they may affect men and women differently, investigators analyzed genetic information from 228,466 women and 195,041 men from the UK Biobank. The Biobank is a major international health resource where half a million people agreed to provide blood, urine, and saliva samples, as well as a detailed history for the purposes of research. Authors of the study used three different obesity measurements:
Overall obesity, defined as a body mass index (BMI) as 30 or greaterFat distribution, as determined by waist-to-hip ratio or the so-called ‘apple’ versus ‘pear’ shapeWaist-to-hip ratio, adjusted by BMI, to determine if and how obesity impacts risk of disease and whether being a man or a woman increases the level of risk
People with obesity weren’t only more likely to have type 2 diabetes and heart disease than those who were not obese — comparatively, they were also at greater risk for chronic obstructive pulmonary disease (COPD), chronic kidney disease, liver diseases, and lung cancer. A higher BMI led to a greater risk of type 2 diabetes in women than in men, whereas a higher waist-to-hip ratio increased risks of chronic obstructive pulmonary disease and chronic kidney disease more in men than in women. There were also some conditions that weren’t associated with obesity, according to the analysis. Colorectal cancer, dementia, hemorrhagic stroke, breast cancer (investigated in women only), and fertility didn’t seem affected by any of the obesity measures, according to the authors. This could be because obesity doesn’t cause any of these conditions, but it could also be due to false negatives because there weren’t enough cases of those conditions to adequately assess an association, investigators wrote. RELATED: 5 Ways to Protect Yourself From a Stroke
Should Doctors Treat Men and Women With Obesity Differently?
This large data set gives us an interesting perspective about how obesity relates to many chronic diseases, says Fatima Cody Stanford, MD, MPH, an obesity medicine specialist at Mass General Hospital in Boston, who wasn’t involved in the study. “There are some differences that appear to exist between the sexes in type 2 diabetes, COPD, and kidney disease. But we still would have significant concern for both men and women who have any of these chronic diseases, and aggressively care for and manage those conditions, including working to improve their weight status to decrease the likelihood of mortality," says Dr. Stanford. “These findings alone wouldn’t change any of my current recommendations to my patients,” she says. Censin says that based on current scientific knowledge, society needs to improve obesity prevention in men and women to help minimize disease risks, Censin says. “However, as research advances we may come to learn that slightly different preventative strategies or drugs work better for one sex, which is why we need to continue researching sex-specific effects,” says Censin. Although this study was designed to look at differences between sexes, Stanford says it was disappointing that participants’ races weren’t considered. “It would have been very interesting to see the differences in disease risk among different races and ethnicities,” says Stanford. “The authors suggest that these findings may have potential implications for public health policies and strategies, but if I were designing strategies, all patients who have these illnesses, regardless of their gender, need aggressive management of their weight,” says Stanford. RELATED: How Your BMI Can Affect Your Health and Wellness
