Two common health problems may form a particularly unhealthy combination in later life.
Adults over 50 who had both a large waistline and vitamin D deficiency were much more likely to die during a six-year study than people who had neither condition.
The study followed more than 5,500 adults and was published in Diabetes, Obesity and Metabolism. It was led by researchers at the Federal University of São Carlos in Brazil in collaboration with University College London.
The scientists used data from the English Longitudinal Study of Ageing, a major research project that follows adults over time. This allowed them to examine how health measurements taken in older age were related to deaths during the following years.
One of the measurements was waist circumference. Researchers increasingly pay attention to waist size because where fat is stored can matter as much as how much a person weighs.
Fat concentrated around the abdomen can surround internal organs such as the liver and intestines. This deep abdominal fat is active tissue that can affect hormones, blood sugar, cholesterol, and inflammatory signals throughout the body.
For this study, abdominal obesity meant a waist larger than 102 centimeters in men or 88 centimeters in women. The second risk factor was vitamin D deficiency, defined as a blood level below 30 nanomoles per liter.
Vitamin D has a familiar connection with bones because it helps the body use calcium. But vitamin D receptors are found in many tissues, and researchers have studied the vitamin’s possible roles in muscles, immune regulation, the nervous system, and cardiovascular health.
Older people can be vulnerable to low vitamin D for several reasons. Aging skin becomes less efficient at making the vitamin from sunlight, and some older adults spend less time outdoors or have diets that provide little vitamin D.
When the researchers looked at the two conditions separately, each was linked with increased mortality. People with abdominal obesity alone had a 47% higher risk of death than those without either risk factor.
Vitamin D deficiency alone was associated with an increase in mortality risk of up to 91%. But participants who had both a large waist and vitamin D deficiency showed the greatest difference.
Their risk of death during follow-up was 123% higher than that of people who had neither condition. In other words, the combined group had more than twice the relative risk.
Researchers believe biology may help explain why these conditions appear together so often. Vitamin D dissolves in fat, and excess body fat can hold some of it inside fat cells.
This may leave less vitamin D circulating freely in the blood. Obesity may also alter enzymes that help the body process vitamin D, potentially reducing the amount available to other tissues.
At the same time, excess abdominal fat can promote chronic inflammation. Unlike the short burst of inflammation that helps fight an infection or heal an injury, long-lasting low-level inflammation can gradually damage tissues and contribute to disease.
Aging itself is also associated with increased background inflammation. When aging, abdominal obesity, and low vitamin D occur together, researchers believe their effects could overlap in ways that place extra stress on the body.
Study coordinator Tiago Silva Alexandre explained that vitamin D helps regulate immune responses. If vitamin D is very low while abdominal fat is already producing inflammatory signals, the body’s ability to control that inflammation may be reduced.
This could potentially contribute to cardiovascular disease, metabolic problems, and loss of muscle. However, the study was not designed to prove the exact biological mechanism behind the higher mortality rate.
The researchers have previously reported links between vitamin D deficiency and physical decline in older adults. Their work suggests that low levels may be associated with weaker muscles, slower walking, and eventually greater difficulty remaining independent.
They have also studied a possible connection between vitamin D deficiency and declining thinking abilities. These findings reflect growing interest in whether vitamin D status can provide clues about several aspects of healthy aging.
Still, vitamin D research has often produced complicated results. Observational studies frequently find that people with low vitamin D have poorer health, but clinical trials of supplements do not always show that raising vitamin D prevents the same problems.
One explanation is that low vitamin D may sometimes be a consequence or marker of poor health rather than its main cause. Someone who is frail or chronically ill, for example, may spend less time outdoors and therefore have lower vitamin D.
The same caution applies to the new study. Researchers observed existing health differences, so they cannot conclude that vitamin D deficiency and abdominal fat directly caused the additional deaths.
The percentages should also be understood correctly. A 123% higher relative risk does not mean that 123% of people with both conditions died, nor does it tell an individual exactly how likely they are to die.
Absolute risk varies greatly depending on a person’s age and health. Heart disease, diabetes, smoking, kidney function, physical activity, medications, and many other factors can change the overall picture.
The study nevertheless has practical value because both waist circumference and vitamin D can be assessed relatively easily. A large waist is already recognized as an important marker of metabolic risk, and doctors can order a vitamin D blood test when appropriate.
People should not respond to the findings by taking very large amounts of vitamin D on their own. Too much vitamin D can raise calcium to dangerous levels and may harm the kidneys and other organs.
Reducing excess abdominal fat is also more complex than simply focusing on body weight. Regular physical activity, nutritious food, adequate sleep, and appropriate medical management of conditions such as diabetes and high blood pressure are established parts of reducing cardiovascular and metabolic risk.
In reviewing the study, its large group of more than 5,500 adults and six years of follow-up make the association worth attention. The finding that the two conditions together identified a particularly high-risk group also supports the idea that health risks can interact rather than acting independently.
The main limitation is equally important: this research cannot prove that treating vitamin D deficiency and abdominal obesity will produce a corresponding reduction in deaths. Intervention trials would be needed to answer that question.
For now, the study is best viewed as evidence that a large waist and very low vitamin D may together signal poorer health after age 50. It gives researchers a strong reason to investigate whether addressing both factors can improve healthy aging and longevity.
Source: Federal University of São Carlos.
