A 5-Minute Guide To Vitamin D: Here's What It Is & Why It's So Important

Unless you live in the tropics year-round (and get outside) or take high-potency supplements proactively (and daily), chances are you aren't getting enough vitamin D—like not even close. And though it's an issue much of the health world is now painfully aware of, vitamin D is scant in foods and one of the most common nutrients gaps1 worldwide.

Vitamin D is both a vitamin and a preprohormone (and full-on hormone in its active form in the body) essential for healthy bodily function.* Often nicknamed "the sunshine vitamin," vitamin D3 is synthesized in our skin via UVB sunlight exposure.

We can also get some (though not enough to impact our vitamin D status in a meaningful way) vitamin D from specific foods.

Vitamin D plays a crucial role in thyroid health as it helps regulate the production of thyroid hormones5,* which have widespread, multifaceted functions in the body including metabolism, weight, mood, the sleep cycle, musculoskeletal health, reproductive health, and immunity. Thyroid hormones also play a role in keeping your hair, skin, and nails youthful and strong.

Pregnancy is another key period to be keenly aware of your thyroid health. To proactively support a healthy postpartum period of recovery, it's best to take care of your thyroid before, during, and after pregnancy―and, given its role in supporting thyroid health, getting enough vitamin D is a great place to start.*

Pregnancy, birth, and caring for a new baby require an increased amount of stress hormones and stamina (and often involve less-than-optimal sleep). This all puts an obvious strain on the body's physiological balance and nutrient reserves. Fetal vitamin D demands lead to increased maternal needs for this critical fat-soluble nutrient.

Optimal vitamin D levels have been shown to positively affect the innate and adaptive immune systems in a variety of ways, including supporting white blood cell function8, helping the immune system adapt to and ward off threats9, and more.*

Vitamin D has been shown to play a role in promoting beneficial gut bacteria, which, in turn, have a positive effect on gut function and metabolism.*

You probably already knew this one, but vitamin D is also critical for your bones because it helps the body absorb and maintains homeostatic balance of calcium and phosphorus, which are essential structural elements of our bones.* For example, in the small intestines, vitamin D works to shuttle the calcium we consume from food into the bloodstream.

The bottom line: Maintaining sufficient vitamin D levels is a must for regulating mineral balance and promoting bone density, strength, and health for life.*

The safest and smartest way to optimize your vitamin D consumption is via high-quality supplementation. To monitor your baseline vitamin D status and track the success of your supplement, you can monitor your blood levels. To do that, have your doctor order a 25-hydroxyvitamin D test, which is also known as the 25(OH)D test. This is the biomarker for vitamin D status in your whole body.

The optimal (not just "normal") amount you want to see, is 50 ng/ml plus. In some cases, even higher levels may be appropriate. The cutpoint to avoid (because it's the cutoff for vitamin D insufficiency12) is 30 ng/ml.

I recommend having your 25(OH)D levels tested twice a year—and perhaps even more often if your health care provider thinks it useful. The benefit of knowing your serum vitamin D status is to track progress and have peace of mind that your vitamin D ritual is achieving and maintaining sufficient levels throughout life.*

The amount of vitamin D you'll need to overcome deficiency or insufficiency and achieve true sufficiency depends upon your individual makeup, body composition, baseline lab test results, and other vitamin D inputs, so check with your health care provider for personalized recommendations on how to keep your levels in check.

As a quick rule-of-thumb, to achieve a 50 ng/ml or higher 25(OH)D lab test result, this will require 5,000 IU of vitamin D3 for most normal-weight adults. Individuals with more weight will need proportionately more vitamin D.12

From there, be sure to protect yourself with nontoxic sunscreen. However, since many people can't safely get enough exposure to move the needle (whether because of an indoor job or where in the world they live), the sun isn't the only answer. And others seek to avoid cumulative sun exposure for other obvious skincare and health risk reasons.

A few foods also contain vitamin D, such as shiitake and button mushrooms (leave them in the sun to elevate their vitamin D levels), mackerel, sockeye salmon, cod liver oil, sardines, and eggs—but consuming them in high enough quantities to meet your nutritional requirements and move the needle on your 25(OH)D levels is a tall, tall order.