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Last updated June 9, 2020. 5 minute read

Can lack of vitamin D cause weight gain?

Studies show that taking vitamin D might somewhat help people who are overweight or obese lose weight, in conjunction with diet and exercise. However, it’s not totally clear if low vitamin D is a cause or effect of excess body weight.

Self Written by Michael Martin
Reviewed by Dr. Mike Bohl, MD, MPH

Being overweight can be a risk factor for vitamin D deficiency. A recent study found that women with higher overall body fat and abdominal (belly) fat and men with high levels of liver and abdominal fat were more likely to be deficient in vitamin D (Rafiq, 2018). And a 2016 review of 15 studies found that a person’s vitamin D level may be “marginally improved” by losing weight (Mallard, 2016).

Some researchers theorize that vitamin D may prevent new fat cells from forming and increase levels of serotonin, a brain chemical that’s associated with appetite. It may also be associated with higher levels of testosterone, which could promote weight loss.

Some studies have found that vitamin D may aid in weight loss or the prevention of weight gain. One study found that overweight or obese women who took a vitamin D supplement for six weeks “significantly decreased” their weight, waist circumference, and body mass index (BMI), compared to a control group (Khosravi, 2018).


  • Science isn’t sure.
  • Studies show that taking vitamin D might somewhat help people who are overweight or obese lose weight, in conjunction with diet and exercise.
  • Excess body fat has also been correlated with a low level of vitamin D.
  • But according to the latest studies, it’s not totally clear if low vitamin D is a cause or effect of excess body weight.

But some studies have found conflicting results. A 2014 study of 218 overweight or obese women found that those who took a vitamin D supplement, along with exercise and a reduced-calorie diet, didn’t lose more weight than women who took a placebo (Mason, 2014).

A 2019 review of 11 randomly controlled trials on vitamin D and weight loss found that taking vitamin D “has a desirable effect on weight loss by reducing BMI and waist circumference in overweight and obese individuals.” But the dosages taken by the study participants varied widely (Perna, 2019). 

The scientific consensus seems to be that none of these results are definitive and that more research is needed. 

So, can a lack of vitamin D cause weight gain? The jury is still out. It’s unclear if vitamin D deficiency can cause obesity or if there is just an association between the two. However, as a group of researchers noted in 2019, “Targeting lifestyle through healthy diet and exercise should be the first treatment option that will affect both obesity-related dysmetabolic state and vitamin D deficiency, killing two birds with one stone” (Vranic, 2019).


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Diagnosing a vitamin D deficiency

Your healthcare provider can check your vitamin D level with a simple blood draw.

According to the National Institutes of Health, you’re at risk for vitamin D deficiency if your blood level of vitamin D is less than 30 nmol/L (<12 ng/mL). You’re at risk of vitamin D inadequacy if your level ranges from 30 to 50 nmol/L (12–20 ng/mL) (NIH, n.d.).

How to get more vitamin D if you’re deficient

Good sources of vitamin D in food include fatty fish (such as salmon and tuna), fish oil, fortified milk, eggs, and fortified breakfast cereals.

You could also take a vitamin D supplement. The Office of Dietary Supplements recommends a daily intake of vitamin D of 600 IU for adults up to age 69 and 800 IU for adults 70 and older. The tolerable upper daily limit is 4,000 IU (100 mcg). Be careful when taking vitamin D supplements—vitamin D toxicity is possible (NIH, n.d.).

What is vitamin D?

Vitamin D is a prohormone—not technically a vitamin—that’s involved in several of the body’s key processes. (A prohormone is something the body makes and converts to a hormone). Known as the “sunshine vitamin,” vitamin D is made by the body as a response to sun exposure. When sunlight hits the skin, the body produces a substance that the liver, then the kidneys, convert to forms that are usable by the body.  

Vitamin D is found in a variety of foods, including eggs and milk. But much of the world’s population is deficient in vitamin D—up to 1 billion people worldwide, and 40% of Americans (Parva, 2018).

Vitamin D’s role in the body/benefits

Bone health/osteoporosis prevention

Vitamin D’s primary role is to help the body maintain the right levels of calcium and phosphorus. It affects how calcium is absorbed from food and how the body builds and reabsorbs bone (which the body is constantly doing; it’s a process called bone remodeling). Studies suggest vitamin D could help prevent fractures and osteoporosis (Bischof-Ferrari, 2005).

Immune function

A lack of vitamin D has been associated with an increased risk of infection and a higher chance of autoimmune diseases. It seems to bolster the body’s innate immune system, helping it destroy bacteria and other invading microbes (Aranow, 2011)

Protection from certain cancers

Some studies have found that vitamin D might have a protective effect against a number of cancers, particularly colorectal and breast (Meeker, 2016). A low vitamin D level is associated with a higher risk of those cancers.

That could be because vitamin D regulates the genes that control cell differentiation, division, and death helps control cell growth, bolsters the immune system, and reduces inflammation—all processes that can affect the development of cancer.

Regulates insulin/reduced risk of diabetes

Regular doses of vitamin D early in life have been found to reduce the risk of type 1 diabetes, and taking vitamin D later in life seems to reduce the risk of type 2 diabetes (Schwalfenberg, 2008). Vitamin D seems to help the body process insulin and control blood sugar.

Cardiovascular health

One study found that vitamin D deficiency is associated with several risk factors for cardiovascular disease, including high blood pressure, coronary artery disease, cardiomyopathy (enlargement of the heart muscle), and diabetes. The study also found that vitamin D supplementation was associated with better survival (Vacek, 2012). However, other studies haven’t found those benefits (NIH, n.d.).