How Low Vitamin D Can Lead to Fatigue and Weight Gain

Although fatigue and weight gain can be attributed to a number of health conditions, as well as lifestyle factors, it might also mean you have a vitamin D deficiency. This nutrient, which your body primarily gets from sunlight, is important for muscle and nerve health as well as fighting disease and illness. Perhaps most important, vitamin D is needed to help the body absorb calcium for strong bones.

Three ounces of cooked salmon provide more than 450 IU, or 11 micrograms, of vitamin D. (Image: AlexPro9500/iStock/GettyImages)

Vitamin D Intake

According to the Office of Dietary Supplements, adults need an average of 600 IU, or 15 micrograms, of vitamin D per day. This nutrient is not widely available in food, but many milk products, orange juices and cereals are fortified with vitamin D. Some foods provide small amounts, such as beef liver, egg yolk, cheese and mushrooms. Fatty fish, such as tuna, contain 0.5 micrograms of vitamin D per ounce.

The body makes the majority of its needed vitamin D from direct exposure to the sun. In fact, a study published in 2017 by BioMed Central Public Health found that people who work the night shift or long hours indoors, such as health care workers, are at higher risk for vitamin D deficiency.

Low Vitamin D and Weight Gain

Research shows that there is a high rate of vitamin D deficiency among people who are overweight or obese; however, there is no proof that one directly causes the other. According to a research review published in 2015 by Obesity Review, obesity is associated with vitamin D deficiency in all age groups around the world.

The same study reports that vitamin D deficiency increases the risk of chronic disease, including excess weight, cardiovascular conditions, cancer, diabetes and high blood pressure. However, this does not take into account lifestyle factors, such as diet, exercise or other medical conditions, that could also lead to weight gain.

Vitamin D and Fatigue

Fatigue is a common side effect of a host of medical conditions, which can make it difficult to determine the underlying cause. However, fatigue has been associated with vitamin D deficiency.

A study published in 2016 by Medicine assessed the effect of a single 100,000 IU dose of vitamin D on self-reported fatigue among otherwise healthy individuals with a vitamin D deficiency. Half of the participants were given vitamin D, while the other half took pills made of sugar alcohol to reduce potential placebo effect. The study showed a significant improvement in fatigue among participants who received the vitamin D capsules.

Supplements and Toxicity

Vitamin D deficiency is typically treated with supplements, but you should consult your doctor to determine the proper dosage before taking vitamin D supplements. Vitamin levels are checked with a simple blood test. Too much vitamin D can be toxic, causing nausea, constipation, confusion, weakness, weight loss, kidney damage and abnormal heart rhythms.

Additionally, medications can interfere with vitamin D absorption. For example, drugs that reduce cholesterol and promote weight loss can decrease the amount of vitamin D that is absorbed by the body. Steroid medications affect how the body processes this nutrient, which in turn lowers calcium absorption, potentially causing bone loss.

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