MADRID — The role of vitamin D in the risk for overweight and obesity has been the subject of multiple studies. Though there’s still not enough evidence to reach a decisive conclusion, several ongoing debates are setting the stage for future research.
Irene Bretón, MD, PhD, discussed these debates in a presentation titled “Vitamin D Deficiency and Obesity: Cause or Consequence?” delivered at the 64th Congress of the Spanish Society of Endocrinology and Nutrition (SEEN). Dr. Bretón is president of the Foundation of the Spanish Society of Endocrinology and Nutrition.
“Vitamin D deficiency can arise from different causes. The percentage that can be attributed to solar radiation is extremely variable. Some studies put it at 80%, while others suggest lower figures. Many diseases have also been associated with vitamin D deficiency or with low vitamin D levels (which are not always at the level of deficiency). Nonetheless, we still have a lot to learn about these associations,” she said.
Dr. Bretón pointed out that many of these studies overlook parathyroid hormone testing. “I also think it’s more appropriate to discuss nutritional status of vitamin D as opposed to serum levels, because these data can be misleading. It would be interesting to focus more on vitamin D metabolism and not just plasma levels.”
Vitamin Deficiency
To answer whether obesity and its complications could be related to low vitamin D levels, Dr. Bretón pointed to this vitamin’s profile in various regions of the world and called attention to the fact that none of the studies on this topic include populations with roughly adequate levels of this vitamin.
“This highlights the prevalence of vitamin D deficiency worldwide. It affects approximately 50% of the population, has been described in all age groups, and affects both men and women — particularly pregnant women and those in menopause — and older adults,” said Dr. Bretón.
She also cited the figures backing this fact: 88% have 25-hydroxyvitamin D levels < 30 ng/mL, 37% have levels < 20 ng/mL, and 7% have levels < 10 ng/mL.
“These percentages have brought us to consider their potential link to the current obesity epidemic. Studies in humans have observed a relationship between low plasma levels and markers for obesity and adiposity. Free 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D are known to be reduced in obesity, and treatments to correct vitamin D deficiency are less effective in people with the disease,” she noted.
Regarding the impact in “the opposite direction,” that is, whether obesity affects the nutritional status of vitamin D, Bretón explained that observational studies have generally found a relationship between overweight and obesity and lower plasma levels of vitamin D. “Data from these studies show that each kg/m2 increase in [body mass index (BMI)] is associated with a 1.15% decrease in 25-hydroxyvitamin D. These studies also show that the prevalence of vitamin D deficiency is 35% higher in patients with obesity and 24% higher in those that are overweight compared with individuals of normal weight. A relationship has been observed between vitamin D deficiency and body fat percentage in men and women and in all age groups,” explained Dr. Bretón.
Dr. Bretón noted that the diseases most closely associated with obesity are type 2 diabetes, hypertension, ischemic heart disease, cancer (colon, breast, prostate, and ovarian), inflammatory liver disease, asthma, and inflammatory diseases.