– Vitamin D is an unusual vitamin because it acts like a hormone in your body. It helps the bones absorb calcium, supports the immune system and may aid strength gain and fat loss.

– Vitamin D is made in the body when your skin absorbs ultraviolet light, but most people don’t get enough sunlight to reach adequate levels

– Deficiency of vitamin D is common, so consuming a D supplement may be beneficial

– The D3 version of the vitamin is absorbed better than D2, making it a wiser choice for supplementation

What Is Vitamin D?

While classified as a vitamin, D is unique among vitamins in a few different ways. For one thing, your body makes it itself when it’s exposed to sunlight. For another, it behaves like a steroid in the body (no, not that kind of steroid), meaning that it can turn genes on and off. This makes vitamin D an especially powerful nutrient with many potential influences on your health.

When your skin absorbs ultraviolet radiation, a cholesterol precursor in your body is converted to vitamin D3 (one type of D vitamin). However, it’s difficult for most people to get the amount of vitamin D they need from the sun alone. Fortunately, vitamin D is available in food, and many other foods are fortified with it. Nevertheless, vitamin D deficiency is common, and a serious threat to health (see Do I Have A Vitamin D Deficiency? below).

Vitamin D is fat soluble, meaning that it dissolves in fats and oils, and can be stored in the body for long periods. For years, scientists have known that Vitamin D promotes the absorption of calcium and phosphate from the food in your gut, making it a key supporter of bone health. More recently, D has also gotten credit for the role it plays in muscle strength and performance, nerve transmissions, and immune health.

How Do Vitamin D2 and D3 Differ?

There are two main kinds of vitamin D—D2 (ergocalciferol) and D3 (cholecalciferol). D2 is found in plant foods, including fungi like mushrooms and yeasts. D3 is only available in animal foods, and it’s the type of vitamin D your body makes on its own when it’s exposed to UV light.

D2 is inexpensive to produce, so it’s often added to foods—such as milk—to boost their vitamin D content. However, D2 is not as well absorbed by the body as D3. Some studies indicate that D3 may be almost twice as effective at raising levels of vitamin D in the blood as D2 (1, 2, 3). If you supplement with vitamin D to achieve optimal levels, nutrition experts generally recommend choosing vitamin D3 supplements.

What Does Vitamin D Do For the Body?

Due to vitamin D’s ability to act like a hormone in the body, it has the ability to support multiple aspects of health. While it’s long been known to help regulate bone health and growth, D has also been linked to the following.


A 2015 meta-analysis of seven studies found that vitamin D supplementation significantly aided gains in upper- and lower-limb strength. The subjects ranged from 18 to 40 years of age.

Weight Management 

A 2014 study followed overweight and obese women on a diet and exercise routine for one year. Half the subjects received a vitamin D supplement, and the other half a placebo. Researchers found that the ones who got up to healthy vitamin D levels lost more weight than the placebo group—by an average of seven pounds.

Meanwhile, another study showed that women who took vitamin D for 12 weeks didn’t lose weight, but their body fat percentages did go down, indicating that D may have helped with re composition.

Immune Health

Innate immunity is the term used to describe the body’s general defense mechanisms—the ones that turn on when it senses that an unwelcome invader has entered your system. Barriers, such as the skin, and white blood cells—the body’s soldiers in the war against a pathogen—are examples of your innate immune defenses.

What Are The Best Sources of Vitamin D?

It’s hard to get enough vitamin D from sunshine, but it’s even harder to get it from food—at least the way most people eat. The best source of dietary D is from fish livers, such as cod liver oil, but now ask yourself… when was the last time you ate cod liver oil?

Mackerel, salmon, sardines, swordfish, trout, and tuna all offer D, as do mushrooms and eggs. If you eat them regularly, you’ll meet the government-recommended requirement, but if you’re in the camp that thinks 600 IU is too low, you’ll need to be more aggressive to hit your D goals. Dairy products and cereals are fortified with vitamin D. © 2021. All rights reserved.