The Role of Vitamin D in Weight Loss: The Science Behind It

February 7, 2024
Green leafy vegetables and a tape measure

The potential relationship between vitamin D in weight loss has been studied for decades. Since vitamin D is a fat-soluble vitamin, people with more body fat may have lower overall vitamin D levels. If more vitamin D is stored in fat, less is available to circulate in the bloodstream.

Some research suggests that weight loss can increase your vitamin D levels.1 This makes sense, but some researchers are questioning whether the reverse is true as well. Does supplementing with vitamin D make it easier to lose weight?

Vitamin D is a fat-soluble vitamin that you mostly get after exposure to ultraviolet light, but you can also get vitamin D from some foods and supplements. Since sunlight is not readily accessible to many people, especially those who live further from the equator, vitamin D deficiency is common.

The Role of Vitamin D

Vitamin D is essential for calcium and phosphorus absorption. It plays an important role in forming and maintaining healthy teeth and bones and supports immune function.

However, emerging research indicates that vitamin D has an important role in many aspects of your health, including maintaining body weight.

Vitamin D Deficiency and Weight Gain

Research has shown an association between vitamin D deficiency and weight gain. Studies have found a link between low levels of vitamin D and a higher body mass index (BMI). This suggests that maintaining optimal levels of vitamin D may be important for managing weight and preventing obesity. However, this may be a chicken-and-egg situation. Having a higher body weight may be the cause of vitamin D deficiency, not the effect.

Vitamin D and Metabolism

Metabolic disorders, such as obesity, are associated with increased inflammation and insulin resistance. Fat tissue, especially the fat surrounding body organs, releases chemicals that increase inflammation.

Insulin is released from pancreatic beta cells. Insulin shuttles glucose from the bloodstream into liver and muscle cells, where it can be used for energy. Chronic inflammation can change insulin signaling, making body cells less sensitive to insulin. This is called insulin resistance.

When your body becomes resistant to insulin, the pancreas pumps out more insulin to compensate, as long as it can keep up. When the pancreas can no longer keep up with the demands, blood sugar gradually rises. This is called type 2 diabetes mellitus.

Vitamin D reduces inflammation and improves insulin sensitivity. However, more research is needed to understand how vitamin D affects pancreatic function and insulin sensitivity.3

Vitamin D and Appetite Control

Vitamin D may impact appetite control and energy expenditure. Low levels of calcidiol (an intermediate form of vitamin D) in the bloodstream may trigger hunger and reduce energy consumption.

Research suggests that the hypothalamus, a key regulatory area of the brain, responds to low calcidiol levels in the bloodstream by increasing appetite and reducing energy expenditure, which can lead to weight gain.

Pills, tape measure and scale

Research on Vitamin D in Weight Loss

Numerous studies have investigated the relationship between vitamin D supplementation and weight loss. Here are some examples of these studies and their reported results.

Study 1: The Effects of Supplementing Vitamin D in Weight Loss

In a study that enrolled 53 individuals with low vitamin D levels and overweight or obesity, half were assigned to receive vitamin D (50,000 IU) and the other half placebo for six weeks while continuing their regular diet. Participants recorded their diet, exercise, and sunlight exposure.

At the end of six weeks, participants taking high-dose vitamin D had decreased weight (3.5 pounds in the vitamin D group vs. 1.1 pounds in the control group), body mass index, and waist circumference.

This was a short study with a small study population. It also occurred at the beginning of summer, which may have impacted vitamin D levels.4

Study 2: Vitamin D and Metabolism

Another study analyzed the data from the VITAL clinical trial. In this clinical trial, researchers from Brigham and Women’s Hospital investigated the effects of vitamin D or marine omega-3 supplements on cancer, heart disease, or stroke.

Researchers were intrigued by the observation that vitamin D supplementation was associated with several significant health benefits for people with a body mass index under 25 (healthy BMI threshold) but not for people with a higher BMI.5

More research is needed to better understand the implications of this study. Since vitamin D is stored in body fat, supplementation to achieve higher levels is not as effective for people with higher BMIs.

Study 3: Vitamin D in Weight Loss

The Vitamin D, Diet, and Activity (ViDA) study enrolled postmenopausal women who were overweight or had obesity and had low vitamin D levels. The treatment group took 2,000 IU of vitamin D daily.

The women consumed a reduced-calorie diet, exercised 225 minutes per week, and met with a dietician regularly. The group taking vitamin D did not have more weight loss than the group taking placebo. However, women who had normal vitamin D levels after supplementation had more weight loss (19 pounds) than women whose vitamin D levels remained low (12 pounds).6

Weight loss benefits from vitamin D may occur only when people reach optimal vitamin D levels. This suggests that adequate vitamin D levels are required for effective weight-loss interventions.

BMI measurements when tracking vitamin D in weight loss

Optimizing Vitamin D in Weight Loss

While more research is needed to better understand how vitamin D levels relate to weight loss, it appears that the benefits may vary depending on your current body weight and ability to restore vitamin D to optimal levels.

Getting Adequate Sun Exposure

The primary source of vitamin D is sunlight. When your skin is exposed to ultraviolet B rays, it triggers the first step in producing vitamin D, converting 7-dehydrocholesterol to pre-vitamin D3. After a few more steps to process vitamin D3, it is transported to the liver through the bloodstream, where it is converted to calcidiol. The final conversion occurs in the kidneys, where calcidiol is converted to calcitriol.

You don’t need a lot of sun exposure to get enough vitamin D; you only need about 20 minutes daily or even just twice per week. UVB radiation is most accessible between 10 a.m. and 4 p.m.

Sunscreen use, geographic location, skin tone, and season all affect whether you can produce enough vitamin D in your body from UVB light exposure.

Incorporating Vitamin D-rich foods

The recommended dietary allowance (RDA) for vitamin D is 600 IU for most adults. However, most people are not getting enough vitamin D. In the United States, about 6% of adults are severely deficient in vitamin D, and 24% of adults have vitamin D levels below the healthy target.2

Older adults, breast-fed infants, people with darker skin pigments or who lack exposure to sunlight, and people with obesity are at increased risk of vitamin D deficiency.

Few foods naturally contain vitamin D. Dietary sources of vitamin D include:

  • Trout, salmon, tuna, and mackerel
  • Cod liver oil
  • Mushrooms
  • Vitamin D-fortified milk
  • Vitamin D-fortified breakfast cereals
  • Sardines canned in oils
  • Eggs

In some cases, supplementation may be necessary to ensure adequate vitamin D levels, especially for people who live in locations with limited sun exposure or who have specific dietary restrictions.

dietary sources of vitamin D

Considering Vitamin D Supplements

If you think you may have vitamin D deficiency (most people do in the winter), talk to your doctor about whether you should have your vitamin D levels tested.

Vitamin D supplements are available in various forms, including capsules, tablets, and liquid drops. Follow the dosing instructions carefully to avoid overdosing. If you are overweight or have obesity and have low vitamin D levels, ask your doctor whether you need to increase your vitamin D intake to reach healthy levels. Excess vitamin D consumption can be toxic, so consult your doctor before exceeding 4,000 IU per day (the upper limit of RDA)


While the scientific evidence surrounding vitamin D’s role in weight loss is still evolving, it appears that optimizing vitamin D levels may have potential weight management benefits. Vitamin D may have an effect on metabolism, appetite control, and body composition, all of which are important in achieving and maintaining a healthy weight.7

The Role of Vitamin D in Weight Loss: The Science Behind It

If you are ready to start a weight-loss treatment plan, talk to a treatment specialist at Invigor Medical. They can help you choose the best plan for you. Ask about vitamin D supplementation as well.

Author: Leann Poston, M.D.
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