A collaborative study by Brazilian and British researchers shows for the first time that obesity can cause a lack of vitamin D and not the other way around. The risk of vitamin D insufficiency and deficiency in subjects with abdominal obesity was 36% and 64% higher respectively than in those without (image: Mohamed Hassan/Pixabay)

Published on 08/14/2023

By Maria Fernanda Ziegler  |  Agência FAPESP — A study conducted by researchers at the Federal University of São Carlos (UFSCar) in Brazil, in partnership with colleagues at University College London (UCL) in the United Kingdom, shows for the first time that the accumulation of abdominal fat is a risk factor for vitamin D insufficiency and deficiency in people over 50.

Considered a hormone, vitamin D performs several functions in the organism, and too little of it can lead to various problems, such as failure to absorb calcium and phosphorus, and impairment of the immune system, for example.

“Both abdominal obesity and vitamin D insufficiency and deficiency are prevalent among older people. However, in this study, we showed that belly fat increases the risk of vitamin D insufficiency and deficiency, and not just the other way around as some studies had already shown. We aren’t saying that lack of vitamin D does not lead to obesity, merely that the accumulation of belly fat is also a pathway to a lack of this vitamin,” said Tiago da Silva Alexandre, a professor of gerontology at UFSCar and last author of an article on the study published in the journal Nutrients.

The study, which was supported by FAPESP, involved analysis of data for 2,459 English people aged 50 and over, who were monitored for four years as participants in the English Longitudinal Study of Ageing (ELSA). 

Vitamin D insufficiency was defined as blood levels between 30 and 50 nmol/L, and deficiency as under 30 nmol/L. To find out how vitamin D levels and abdominal obesity correlated, the researchers selected ELSA participants with normal levels of vitamin D (more than 50 nmol/L) and divided them into two groups: with little abdominal fat and with an above-normal waist circumference (more than 102 cm for men and more than 88 cm for women). 

“An analysis of their vitamin D levels four years after the first data collection wave showed the risk of vitamin D insufficiency and deficiency in subjects with abdominal obesity to be 36% and 64% higher respectively than in those without,” Alexandre said.

The role of aging

The link between lack of vitamin D and obesity had been confirmed in previous research, he added. “But these studies were based on body mass index [BMI] using height and weight, with a general view of obesity and a lack of precision. The question is why so many countries have such a high prevalence of vitamin D deficiency whether or not they have plenty of sunshine. The answer is high prevalence of obesity,” he said.

The body obtains vitamin D from food and sunlight. A precursor of the vitamin is stored in the deepest layers of the skin. The structure of the skin is modified by sunlight, and various metabolic processes convert the precursor into active vitamin D.

Changes in body composition, including a build-up of belly fat, naturally occur during aging. The skin also becomes thinner, so that less of the precursor may be available in older people, who also tend to synthesize less vitamin D.

“In our study, we used waist circumference because it’s easy to measure and serves as an indicator of belly fat. It’s more precise than BMI, for example,” Alexandre said.

Aging is accompanied by reduced cutaneous synthesis of vitamin D and decreased expression of vitamin D receptors in tissues in general. Moreover, vitamin D can become trapped in adipose tissue owing to strong expression of vitamin D receptors in this tissue, leading to a significant reduction in its bioavailability. 

“Our analysis of these people’s adipocytes [fat cells] showed low levels of vitamin D enzymes. This happens because a vitamin D receptor captures vitamin D from the bloodstream to compensate for low levels of the enzymes in fat cells. Simply put, it’s as if adipose tissue ‘hijacks’ the vitamin D. The reduced bioavailability shows up in blood work as vitamin D insufficiency or deficiency,” said Thaís Barros Pereira da Silva, first author of the study with a scientific initiation scholarship from FAPESP.

The study reinforces the need for public policies to prevent and combat both obesity and lack of vitamin D in older people, Alexandre added. “We all know prevention is better than cure. Our research shows that abdominal obesity can interfere with blood levels of vitamin D. Lack of this prohormone can lead to a number of health problems in older people,” he said.

The article “Is abdominal obesity a risk factor for the incidence of vitamin D insufficiency and deficiency in older adults? Evidence from the ELSA study” is at: www.ncbi.nlm.nih.gov/pmc/articles/PMC9572900/. 

 

Source: https://agencia.fapesp.br/42127