Investigators in Italy sought to determine the relationship between visceral adipose tissue and vitamin D levels, particularly examining the potential threshold for vitamin D storage and sequestration using adipose tissue.
Their findings suggest that in visceral adipose tissue vitamin D is stored, but may become trapped, leading to its reduced availability for metabolic processes. These results support the hypothesis that adipose tissue acts both as a potential reservoir and sequestration site for vitamin D, the researchers said.
They added: “The storage or sequestration of vitamin D in adipose tissue may have implications for individuals with obesity or abdominal obesity, as they are more likely to have insufficient or deficient vitamin D levels. This finding aligns with previous studies that have shown an inverse relationship between abdominal obesity and vitamin D levels.”
Vitamin D levels and obesity
Fifty-eight people participated in the study who had various ailments including cardiovascular diseases, hypertension, diabetes, fatty liver disease and venous thromboembolic events. The scientists excluded participants taking drugs that could alter bone metabolism or who were affected by metabolic diseases.
The participants underwent blood sampling to evaluate calcium and vitamin D levels at baseline and after 6 months of supplementation with 50,000 IU of vitamin D per month. Using ultrasonography, the researchers evaluated subcutaneous adipose tissue thickness, visceral adipose tissue, preperitoneal adipose tissue, prerenal adipose tissue waist-to-hip ratio, and waist-to-height ratio. In addition, they calculated the body adiposity index, using the size of the hips compared to the person's height.
For males, there was a relationship between vitamin D levels at follow up and waist circumference at baseline. In females, the best predictor of the vitamin D level at the end of the study was the waist-to-hip ratio.
An analysis of the effects of vitamin D supplementation revealed that a smaller proportion of males (38%) and females (17%) achieved normal vitamin D levels, particularly among subjects with higher visceral adipose tissue.
“These findings suggest that different anthropometric variables may influence vitamin D status in males and females,” the researchers said.
After 6 months of supplementation, the mean increase in vitamin D levels was 9.6 ng/mL, with 55.2% of subjects becoming deficient.
These results imply that abdominal obesity, specifically visceral adipose tissue, may play a crucial role in vitamin D homeostasis, as previously suggested by others, the scientists said.
Global health problem
Vitamin D deficiency and insufficiency are significant global health concerns. Low outdoor physical activity and subsequent low sun exposure, poor dietary intake of vitamin D, obesity and especially abdominal obesity are involved in the cause of vitamin D deficiency.
More research demonstrates that abdominal obesity, assessed with waist circumference, is associated with metabolic syndrome and has been linked to low vitamin D levels.
However, “the relationship between vitamin D and adipose tissue is intricate, and the role of adipose tissue in regulating circulating vitamin D levels is not clear, particularly whether it acts as a reservoir or sequestration site for the vitamin,” the scientists said. “Certain researchers have noted that the expanded fat tissue in obese individuals can function as a storage site for vitamin D. This heightened demand for vitamin D to fill this reservoir may potentially lead to insufficient levels of serum vitamin D in obese individuals.”
Despite a lack of knowledge regarding the role adipose tissue plays in regulating vitamin D circulation, addressing the worldwide prevalence of vitamin D deficiency and insufficiency requires a multifaceted approach, the researchers said.
“Public health initiatives should focus on promoting outdoor physical activity and sun exposure, particularly in regions with limited sunlight during certain seasons. Nutrition education programs can help individuals make informed dietary choices to increase their vitamin D intake,” the added. “Additionally, healthcare professionals should be vigilant in assessing the vitamin D status of patients, especially those with obesity-related conditions, and recommend appropriate supplementation when necessary.”
“Unraveling the Connection: Visceral Adipose Tissue and Vitamin D Levels in Obesity”
Authors: Mattia Cominacini et al.