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Overweight people have difficulty with utilizing vitamin D

Overweight people have difficulty with utilizing vitamin DVitamin D is important for multiple metabolic processes. However, overweight individuals have difficulty with activating the form of vitamin D that we get from supplements, and that impairs their utilization of the nutrient. Therefore, vitamin D supplements work differently on those who take them to prevent diseases like cancer, diabetes, and autoimmune diseases, according to a large American study called VITAL. A group of scientists looked closer at the study and found that overweight people may have an increased need for vitamin D.

Most of the body’s cells have vitamin D receptors (VDR), but it is an inactive form of vitamin D that we get from supplements or synthesize in our skin in response to sunlight. Normally, the inactive vitamin D must be converted in the liver and kidneys and various cells into the active steroid form of the vitamin. This form of vitamin D is the one that initiates various gene activities and metabolic processes. Therefore, it is of vital importance to the cells that need vitamin D that the vitamin is properly metabolized in advance.
A team of scientists from Brigham and Women’s Hospital in Boston, USA, has found new evidence suggesting that vitamin D is metabolized differently in overweight people, those with a high BMI, compared with people of normal weight. Their study is published in JAMA Network Open and is based on an analysis of a previously published American population study called VITAL with more than 25,000 participants. As part of the VITAL study, scientists looked at several parameters with relation to the participants’ background and lifestyle, and whether supplementation with vitamin D or fish oil could lower their risk of cancer, cardiovascular disease, and stroke. Blood levels of vitamin D and omega-3 fatty acids were measured as part of the study.
According to this study, supplements of vitamin D were able to lower the risk of cancer, heart failure, and stroke. Fish oil supplementation was particularly effective for reducing the risk of cardiovascular disease. It turned later that the two supplements could also lower the risk of autoimmune diseases. Interestingly, it appeared that BMI played a determining role.

  • BMI (Body Mass Index) shows the relation between height and weight
  • Underweight: Under 18.5
  • Normal: 18.5 – 25.0
  • Overweight: 25.0 – 30.0
  • Obese: Over 30

Vitamin D only prevents diseases in people with normal BMI

In their analysis of the original VITAL study, the scientists observed that vitamin D supplementation only had a preventative effect on cancer, cardiovascular disease, stroke, and autoimmune diseases in people whose BMI was below 25.
The researchers refer to other studies where vitamin D supplements given to type 2 diabetics did not appear to have the expected effect. In their analysis of the VITAL study, the scientists therefore looked at the relation between BMI and the effect of vitamin D among 15,515 of the original study participants. They measured total vitamin D, circulating vitamin D, and different vitamin D markers, including metabolites such as calcium and parathyroid hormone that help the body utilize vitamin D.
According to the researchers, most studies only focus on total levels of vitamin D in the blood. But looking at the different metabolites and biomarkers has given them new insight into how the body metabolizes vitamin D.
The scientists conclude that BMI is closely related to the body’s response to vitamin D supplementation. This may explain why overweight people and diabetics have difficulty with utilizing vitamin D.

Why do overweight and diabetic people have difficulty with utilizing vitamin D?

An earlier study of mice, which is published in News Medical Life Sciences, shows that overweight mice have difficulty with utilizing vitamin. Apparently, the mice have lower levels of a liver enzyme that is important for the body’s vitamin D metabolism.
Many overweight people also suffer from metabolic syndrome and non-alcoholic fatty liver disease (NAFLD), which makes it increasingly difficult for them to metabolize vitamin D in their liver and to activate vitamin D in the kidneys and in other tissues. The same goes for people with type 2 diabetes.
The poor vitamin D utilization becomes a vicious cycle, also because vitamin D is essential for our blood sugar balance and weight. The scientists behind the new study therefore conclude that overweight people and diabetics have an increased need for vitamin D.
Another study that is published in Advanced Biomedical Research shows that overweight people and type 2 diabetics may also need more magnesium. Magnesium, by way of different enzyme processes, helps to metabolize vitamin D in the liver, the kidneys, and in other tissues. Magnesium is found in various foods such as dark leafy greens. When taking magnesium in supplemental form, make sure to choose a preparation with good absorption.

  • The recommended daily intake for vitamin D is 5-20 micrograms
  • Overweight and diabetes may increase the need for vitamin D
  • It is possible to buy vitamin D supplements with as much as 100 micrograms (which is the safe upper intake level)
  • Magnesium is important for the metabolism of vitamin D


Deirdre K. Tobias, Heike Luttmann-Gibson, Samia Mora, Jacqueline Danik, Vadim Bubes, Trisha Copeland, Meryl S. LeBoff, Nancy R. Cook, I-Min Lee, Julie E. Buring, JoAnn E. Manson. Association of Body Weight With Response to Vitamin D Supplementation and Metabolism. JAMA Network Open, 2023

Brigham and Women´s Hospital. Vitamin D benefits and metabolism may depend on body weight. ScienceDaily January 15, 2023

Jill Hahn et al. Vitamin D and marine omega-3 fatty acid supplementation and incident autoimmune disease: VITAL randomized controlled trial. The BMJ 26 January 2022

Kate Anderson. Vitamin D supplementation less effective in presence of obesity shows study. News Medical Life Sciences. Feb. 2022

Azadehalsadat et al. The Therapeutic Effects of Magnesium in Insulin Secretion and Insulin Resistance. Advanced Biomedical Research 2022

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