How Vitamin D Affects Body Fat Percentage

Does Low Vitamin D Make You Fat?

You know what vitamin D does for your overall health, but what about your body composition? Check out this study.

Back in 2020, scientists lined up 47 college athletes to test the fat-loss effects of training and concurrent daily usage of 1,000 IU of vitamin D. They did the blood work and the scans for the three-month study, and then, one month into the project, COVID hit. Gyms shut down. The previously fit athletes stopped training. However, 27 of them kept taking the vitamin D they'd been supplied.

After three months, the scientists re-examined the athletes just to see what happened. The athletes who didn't take vitamin D during the shutdown increased their fat percentage by 1.9 points. But those who did take vitamin D only increased their fat percentage by 0.2 points. (1)

That's a big difference. The scientists came to the following conclusion: "Vitamin D supplementation might have preferable effects on maintaining athletes' body composition under circumstances where sports activity has decreased."

Were They on to Something?

This study had some limitations due to the lockdown. Fortunately, other studies on vitamin D and fat loss give this particular study more credence. Arunabh, et al. found that body fat percentage is inversely related to serum vitamin D3 levels. (2) Another study found that increasing vitamin D levels by supplementation led to body fat reduction. (3)

Add the current study where vitamin D (Buy at Amazon) plays a role in maintaining fat percentage even during periods of inactivity and that's a pretty compelling case to take vitamin D.

Other Reasons Athletes Should Take Vitamin

Vitamin D supplementation can make you leaner or keep you lean, but the vitamin's resume is much longer, particularly in athletes:

  • Vitamin D and Skeletal Muscle: Having optimal levels of vitamin D increases muscle protein synthesis, jump height, the production of ATP, and the overall capacity to perform both aerobic and anaerobic exercise.
  • Vitamin D and Lung Function: Low levels of vitamin D correlate strongly with reduced lung capacity. Optimum levels of vitamin D, however, ensure healthy lung structure, capacity, optimal oxygen exchange, and the ability to finish a task without wheezing.
  • Vitamin D and the Heart: Without proper levels of vitamin D, arteries get stiff and atherosclerosis is a definite possibility. Your circulatory system starts to have the pliability of a cheap garden hose.
  • Vitamin D and Sex: Women who have high(er) levels of the vitamin have higher circulating levels of estradiol, testosterone, FSH, LH, and DHEA, which, logically, can lead to being more orgasmic. Similarly, vitamin D supplementation significantly (53.5 nmol/l) increases testosterone levels in men, at least according to one study.

The Problem with Vitamin D Supplementation

Vitamin D doesn't work – at least as far as the immune system is concerned – if there aren't sufficient levels of magnesium in the body to help it. It's hard to substantially raise vitamin D levels in the body unless magnesium is there to coax it along.

Most Americans – 80% by some estimates – are deficient in magnesium, and it's even worse in athletes because the mineral sneaks out of the body through sweat. In fact, it's this widespread magnesium deficiency that might be responsible for most vitamin D deficiencies in the first place.

Two clinical studies on magnesium-deficient patients found that magnesium infusion alone brought up levels of 25(OH)D (a prehormone that's produced in the liver by hydroxylation of vitamin D3) and 1,25(OH)2D (the active form of vitamin D in the body) a little bit, whereas magnesium infusion plus oral vitamin D substantially increased serum levels of 25(OH)D and 1,25(OH)2D. (4, 5).

In two other studies involving patients suffering from vitamin D rickets, magnesium supplementation decreased resistance to vitamin D treatment, whereas intramuscular infusion of high amounts of vitamin D alone (up to 600,000 IU) didn't do squat.

What to Do

Make sure you're getting sufficient levels of magnesium in your diet and take a vitamin D supplement (Buy at Amazon).

As far as magnesium, eat a ton of Swiss chard and seaweed. Yeah, okay, most of us aren't willing to eat the amounts of the magnesium-rich foods it would take to get us to a gram (e.g., about 10 cups of seaweed). To play it safe, think about going the supplement route. Elitepro (Buy at Amazon) is a solid choice.

ElitePro Minerals

Concerning vitamin D, achieving or maintaining therapeutic levels is tricky, even with magnesium's help. That's why taking microencapsulated vitamin D3 (Buy at Amazon) (choleocalciferol) is a good idea. The vitamin presents as tiny, water-dispersible "beadlets." This microencapsulated vitamin D3 is the most bioavailable and longest-lasting form. Its effects remain constant for up to 14 days, making it a lot better than the oil-based vitamin D3 supplements that make up most of the market.

Most experts recommend dosages up to 5,000 IU a day. You can get microencapsulated vitamin D in Biotest's D Fix (Buy at Amazon). D Fix technology solves the biggest problem with Vitamin D supplements – absorption.

Buy D Fix High-Absorption Vitamin D at Amazon


  1. Kawashima I et al. "The impact of vitamin D supplementation on body fat mass in elite male collegiate athletes." Nutr Metab. 20211;18:51.
  2. Arunabh S et al. "Body fat content and 25-hydroxyvitamin D levels in healthy women." J Clin Endocrinol Metab. 2003 Jan;88(1):157-61. PubMed: 12519845.
  3. Salehpour A et al. "A 12-week double blind randomized clinical trial of vitamin d3 supplementation on body fat mass in healthy overweight and obese women." Nutr J. 2012 Sep 22;11:78. PubMed: 22998754.
  4. Dai Q et al. "Magnesium status and supplementation influence vitamin D status and metabolism: results from a randomized trial." Am J Clin Nutr. 2018 Dec 1;108(6):1249-1258. PubMed: 30541089.
  5. RosanoffA et al. "Essential Nutrient Interactions: Does Low or Suboptimal Magnesium Status Interact with Vitamin D and/or Calcium Status?" Adv Nutr. 2016 Jan 15;7(1):25-43. PubMed: 26773013.

Is supplementation the end? I live in the high desert (about 5000 feet). Winters can be brutal. At times -25/-30° F. This summer I have been taking 20 minute sun baths 3-4 days a week. The tan is good, but I do feel good. I feel more energetic. Post workout DOMS seems to be less intense. And at 60 that is a benefit.

I have always thought sunlight helps reduce appetite, or without doing research, I have wondered if sun baths (brief 15-20 minutes) increase Vit D enough to enhance mood, and have a hand in weight control?