Vitamin D: Benefits, Sources, and Dosage

Updated on September 6th, 2020
best types of vitamin d

Vitamin D, also termed the “sunshine vitamin” because it’s produced within the body when the skin is exposed to the sun. But many turn to supplements in cooler months of the year when dark and cold days restrict time spent outdoors.

What Is Vitamin D?

Unlike water-soluble vitamins, Vitamin D is a fat-soluble vitamin – which means any excess is stored in the body rather than flushed out with urination – that’s found naturally in some foods and added to others.

Our body could also synthesize vitamin D when exposed to the sun’s UV (ultraviolet) rays, but some gene variants can prevent this from happening in some people’s bodies.

When vitamin D gets into our body, it turns it into a hormone, which is sometimes called calcitriol or activated vitamin D, according to the Vitamin D Council, a nonprofit that educates consumers and health professionals about the nutrient.

Minimizing vitamin D levels isn’t just a winter problem. Over the past few decades, American people with sufficient levels have reduced. Adults achieving vitamin D adequacy have dropped from sixty percent in the early 1990s to thirty percent in the early 2000s, according to a study by the CDC (Centers for Disease Control and Prevention) data.

Moreover, levels of vitamin D sufficiency among African Americans dropped from 10 percent to only 5 percent during the same period. (1)

Definitions of precisely what vitamin D deficiency means vary from equal to or less than 12 nanograms per milliliter (12 ng/mL) to equal to or less than 20 ng/mL on the high end. Using the upper measure, studies suggest 41.6 percent of Americans have a vitamin D deficiency.

Those who are obese, nonwhite, or without a college education are at higher risk of not having sufficient vitamin D levels. (2)

Using sunscreen and drinking less milk (a beverage that has been fortified with vitamin D since the 1930s) are among the reasons that Americans’ Vitamin D status has dropped over the decades. Indeed, the NIH (National Institutes of Health) notes that deficiency has become more prevalent in men in particular, likely due to reduced milk drinking, rising weight, and excessive outdoor sunscreen usage. (3

That drop is an issue because the vitamin can help the gut absorb calcium, promoting healthy and strong bones. Vitamin D is also helpful in boosting cell growth and immune function and reducing inflammation. 

[Also Read: Vitamin D for Bones]

The Different Types Of Vitamin D

The term ‘vitamin D’ refers to not one, but multiple different forms of the vitamin. Two forms are necessary for humans: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D3 is naturally synthesized in our skin through exposure to the sun’s UVB (ultraviolet B) rays, whereas plants synthesize vitamin D2. Both Vitamin D3 and Vitamin D2 are biologically inactive forms of Vitamin D. Before they can become active in our body, they must be converted to active forms in the kidneys and liver.

How Much Vitamin D Should You Be Receiving?

Adults require 600 IU (international units) of vitamin D each day (800 IU if you’re over 70), which can be sourced through diet, sunlight, or supplements. 

Vitamin D2 — the plant-sourced form of vitamin D, is naturally found in mushrooms. Food sources that contain vitamin D3 comprise fatty fish, such as tuna, salmon, and mackerel; fortified milk and other dairy products; fish liver oils; and egg yolk. 

Yet very few foods have adequate vitamin D to reach prescribed daily intakes, and sunshine can be unreliable in specific climates. Depending on sourcing vitamin D through diet alone, women and men usually don’t exceed 288 IU daily on average. Even drinking a glass of milk(8-ounce) will only get you 100 IU — 1/6th the amount that many adults require daily. 

But when supplements are incorporated, they get closer to the 600 IU goal. Consider this: Women aged between 51 and 70, who averaged 156 IU through the diet-only approach, reached 404 IU with the aid of supplements. 

[Also Read: Could Vitamin D Decrease Your Risk Of Covid-19?]

What does vitamin D deficiency cause?

Vitamin D deficiency is most strongly related to weak bones. Severe vitamin D deficiency causes skeletal deformities and soft bones in children (more generally called rickets) and can cause osteomalacia (weak bones in adults). Low bone mass and structurally weak bones (osteoporosis) are related to low calcium and vitamin D levels.

Though not as well recognized, low vitamin D levels have also been linked with immune function and frailty and falls in the elderly and chronic diseases, including heart disease, colon cancer, and diabetes (remember, though, that linking does not equal causation!).

Few groups of people are at greater risk of vitamin D deficiency.

  • Older adults. Adult skin does not synthesize vitamin D as efficiently, and older adults often spend more time indoors, restricting their sun exposure.
  • Exclusively breastfed infants. Human milk does not contain enough vitamin D.
  • Individuals with darker skin. The increased quantity of melanin pigment decreases the skin’s ability to synthesize vitamin D.
  • People with gastric bypass or certain gastrointestinal conditions. Gastrointestinal conditions or gastric bypass procedures can reduce your ability to absorb the vitamin.  
  • People taking specific medications. If you’re taking steroids, some anti-seizure medications, some weight loss drugs, they can affect Vitamin D levels.

Should I get my vitamin D levels checked?

There’s little evidence to support getting vitamin D levels checked if you’re an otherwise healthy individual.

So, what can you do? Talk to your physician about the intake of vitamin D supplements if you’re concerned that you’re not getting adequate amounts. For adults older than sixty-five, there is some evidence that vitamin D can reduce falls risk. Still, recent research indicated that vitamin D supplements might not protect against bone fractures.

Bottom Line 

Finally, no matter which group you fall into, the finest way to support healthy bones is through a healthy lifestyle and diet that includes natural sources of vitamin D and calcium and weight-bearing exercises, not smoking and avoiding too much alcohol. 

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