Having too much fat around the waist and very low vitamin D levels at the same time may be especially risky after age 50.
A large study found that people with both conditions had more than twice the risk of dying during the study period compared with people who had neither.
The research included 5,520 adults aged 50 and older and was published in the journal Diabetes, Obesity and Metabolism. Scientists from the Federal University of São Carlos in Brazil worked with researchers from University College London on the study.
The researchers followed participants for six years using information from the English Longitudinal Study of Ageing. This major long-term project collects health, social, and economic information from adults as they grow older.
The team was interested in two common health problems: abdominal obesity and vitamin D deficiency. Both have previously been linked with poorer health, but the researchers wanted to know what happens when they occur together.
Abdominal obesity means carrying a large amount of fat around the waist and internal organs. In the study, it was defined as a waist circumference above 102 centimeters for men and above 88 centimeters for women.
Waist size can provide information that body weight alone may miss. Fat stored deep in the abdomen, particularly around internal organs, is more strongly connected with inflammation, insulin resistance, diabetes, and cardiovascular disease than fat stored in some other parts of the body.
Vitamin D is best known for helping the body absorb calcium and maintain healthy bones. However, it also acts more like a hormone than a simple vitamin and has effects on muscles, immune activity, and many other tissues.
The body can make vitamin D when skin is exposed to sunlight, and smaller amounts can come from food or supplements. Levels can become low for many reasons, including limited sun exposure, older age, darker skin, some medical conditions, and dietary factors.
In this study, vitamin D deficiency was defined as a blood level below 30 nanomoles per liter. Researchers then compared deaths among people with abdominal obesity, vitamin D deficiency, both conditions, or neither.
Abdominal obesity alone was associated with a 47% higher risk of death during follow-up. Vitamin D deficiency by itself showed an even stronger association, with the risk increasing by as much as 91%.
The largest difference appeared among people who had both problems. Their risk of death was 123% higher than among participants with neither abdominal obesity nor vitamin D deficiency.
Study coordinator Tiago Silva Alexandre of the Federal University of São Carlos said the two conditions may reinforce each other. One possible explanation involves the way vitamin D behaves in people who carry excess body fat.
Vitamin D is fat-soluble, which means it can be stored in fat tissue. In people with obesity, more vitamin D may become held within fat cells rather than remaining freely available in the bloodstream for use elsewhere in the body.
Obesity may also change the activity of enzymes involved in processing vitamin D. Together, these effects could help explain why people with obesity frequently have lower circulating vitamin D levels.
At the same time, abdominal fat is biologically active tissue. It can release substances that promote ongoing low-level inflammation and contribute to problems with blood sugar, blood pressure, and blood vessels.
Vitamin D also interacts with the immune system and may help regulate inflammatory responses. The researchers suggest that having both abdominal obesity and vitamin D deficiency could therefore create a less favorable environment than either problem alone.
This possibility may be especially relevant in older adults. Aging is often accompanied by a gradual rise in low-level inflammation, sometimes described by researchers as age-related chronic inflammation.
When excess abdominal fat is added to that background inflammation, the body may face additional stress. Low vitamin D could potentially make it harder to keep some inflammatory processes under control, although the exact biological pathways still need more study.
The research group has previously examined vitamin D in relation to other aspects of aging. Their earlier work has linked deficiency with reduced muscle strength, slower walking, loss of independence, and greater risk of cognitive decline.
These findings do not mean vitamin D deficiency necessarily causes all of these problems. Low vitamin D can also be a marker of poor health, reduced outdoor activity, chronic illness, or other factors that themselves raise health risks.
That distinction is particularly important when interpreting the new mortality study. It was observational, meaning researchers measured naturally occurring differences among people rather than randomly assigning participants to have different vitamin D levels or waist sizes.
As a result, the study can show a strong association but cannot prove that taking vitamin D supplements or losing abdominal fat will directly reduce a person’s risk of death by the percentages reported. Other health and lifestyle differences may contribute to the pattern.
The 123% figure also describes relative risk rather than an individual’s absolute chance of dying. A person’s actual risk depends on age, existing diseases, smoking, physical activity, blood pressure, diabetes, and many other factors.
Even with these limitations, the study highlights two potentially modifiable areas of health that are easy to monitor. Waist circumference can be measured simply, while vitamin D levels can be checked with a blood test when there is a medical reason to do so.
The results should not be taken as a reason for everyone over 50 to start high-dose vitamin D supplements. Excessive vitamin D can be harmful, and testing or supplementation is best discussed with a healthcare professional based on individual risk and medical guidance.
In reviewing the findings, the most important observation is that the combination of abdominal obesity and severe vitamin D deficiency identified a group with particularly high mortality risk. The study is strengthened by its large sample and six-year follow-up, but it cannot establish cause and effect.
Future research will need to determine whether actively correcting vitamin D deficiency, reducing abdominal fat, or doing both actually lowers mortality. Until then, the findings provide a useful warning that several common health risks may become more important when they occur together rather than in isolation.
Source: Federal University of São Carlos.
