Vitamin D remains one of the body’s most essential nutrients required for proper organ and system functioning. It’s also super essential for bone strength and boosting the immune system. While some people obtain adequate amounts of it from food, a deficiency of it could be fixed by taking supplements. Now, a new study has revealed that the body’s ability to properly process these supplements depends on just how much you weigh. 

According to new research from Brigham and Women’s Hospital, being overweight, usually reflected by a high BMI, can affect how your body metabolizes vitamin D supplements resulting in only very little of the abundant benefits the vital nutrients provide being gained. 

Obesity, a disorder characterized by a body mass index of 30 or higher has seen a rise significant rise in cases in recent years particularly in children between the ages of 5 and 19 with WHO reporting an increase from 4% to 18% globally from 1975 to 2016. Asides from the obvious health risks like heart disease, diabetes, and so on, the metabolism of certain drugs and supplements has been observed to take a different turn in obese individuals.

A recent study conducted to ascertain the benefits of vitamin D supplementation reported a 30 to 40 percent reduction in cancer-related deaths and autoimmune disease—a result not observed in participants with a high BMI who had taken similar doses of supplements, encouraging a more in-depth analysis. 

“This study sheds light on why we’re seeing 30-40 percent reductions in cancer deaths, autoimmune diseases, and other outcomes with vitamin D supplementation among those with lower BMIs but minimal benefit in those with higher BMIs,” says study’s senior author JoAnn Manson, MD, DrPH.

Study Methodology

To arrive at their findings, the study’s authors analyzed blood samples obtained from over 16.000 individuals who had participated in a previous VITAL study, aimed at identifying the benefits of vitamin D. Participants in the previous study had been split into two groups, with one group given supplements and the other given placebos and then the benefits of the tested for after a two-year observational period. 

Blood samples provided by participants in each of four weight categories in the VITAL study – normal weight, overweight, obese class 1, and obesity class 2, provided at the beginning and the end of the study were analyzed using several assay techniques to determine vitamin D levels as well as the presence of biomarkers like metabolites, calcium, and parathyroid hormones, etc. 


The results showed that taking vitamin D supplements corresponds to an increase in vitamin D biomarkers produced regardless of weight as all participants recorded higher levels of vitamin D, calcium, parathyroid hormone, and other biomarkers tested for. 

They did however observe that the quantity of these biomarkers was significantly lower in obese participants than in their normal-weight counterparts. The result also reflected an even more massive decline over the two-year observational period.

“There seems to be something different happening with vitamin D metabolism at higher body weights, and this study may help explain diminished outcomes of supplementation for individuals with an elevated BMI.”


Proper absorption, distribution, and metabolism of drugs—including supplements—have been known to be affected by food, genetics, and co-existing disorders with obesity remaining a prime example of such disorders.

The diminished outcomes of supplementation observed in the study go a long way to emphasize the need for an alternative dosing system for at-risk populations.

Written by

Medically Reviewed by