Vitamin D: A Reason to Bask in the Sun

Updated: May 30

While the title may imply we're suggesting that you grab your favorite beach towel and head to the beach as fast as you can, we're not advising a two to three hour sun bathe to get as tan as you can. We're simply suggesting a 15 to 30 minute walk or relaxation in the sun, with its beautiful rays beaming down on you, as a part of your daily health habits. This practice can stimulate vitamin D synthesis in your body, which supports bone, heart, immune, and mental health.

Are you getting enough?

Vitamin D is well known for supporting bone health. However, research is showing it plays a role in so much more from supporting heart health to immune function to fertility to mood. Vitamin D deficiency is defined as vitamin D levels less than 30 nmol/L while vitamin D insufficiency is defined as vitamin D levels between 30 to 50 nmol/L. Vitamin D deficiency affects about one billion people worldwide, while 50 percent of the population has vitamin D insufficiency. Factors that affect vitamin D status include diet, exposure to sunshine, geographical location, skin pigmentation, malabsorption, and kidney or liver disease. Ensuring you're getting enough through sun exposure, diet, or supplementation is important for optimal health. How do you know? Let's dive in...

But First—What is Vitamin D?

Vitamin D is a fat-soluble vitamin with many important physiological functions in the body including promoting bone health, muscle function, immune function, cardiovascular health, and has also been found to be an important modulator of the reproductive system and fertility. Vitamin D has two primary forms, vitamin D2 and D3, but many other types of vitamin D form through metabolism. Vitamin D can be obtained through some foods, exposure to sunlight, or supplementation. Vitamin D2 (ergocalciferol) is derived from fortified and plant sourced foods. In the past, vitamin D3 was only derived from animal sourced foods and exposure to sunlight. However, vegan vitamin D3 supplements, made from lichen (a type of algae) are now available. Vitamin D3 (cholecalciferol) is the more readily absorbed form of vitamin D.

Science Alert!

When skin is exposed to UVB radiation, 7-dehydrocholesterol (a cholesterol precursor) in the skin is converted to vitamin D3. Both vitamin D3 and vitamin D2 are metabolized to 25-hydroxyvitamin D (abbreviated as 25(OH)D), the major circulating metabolite, or form of vitamin D, in the liver. If there is a need for vitamin D in the body, 25(OH)D is then converted to 1,25-dihydroxyvitamin D (abbreviated as 1,25(OH)2D) in the kidneys, which is the active form that exerts physiological functions and is characteristically a steroid hormone. Both the kidneys and liver play critical roles in maintaining optimal levels of vitamin D, which is why individuals with kidney or liver disease may have suboptimal vitamin D levels.

Who's At Risk?

The serum level of 25(OH)D is measured to determine the adequacy of vitamin D status. The Institute of Medicine (IOM) has defined four categories of vitamin D status including risk of deficiency, risk of inadequacy, sufficiency, and above normal, which may be reason for concern. A 25(OH)D serum level of less than 30 nmol/L is associated with vitamin D deficiency; a serum level of 30–50 nmol/L is considered insufficient; a level greater than 50 nmol/L is considered adequate; and a serum level greater than 125 nmol/L is linked to adverse effects. Data from 2011–2014 found that 18 percent of individuals in the United States were at risk of insufficiency, while 5 percent were at risk of deficiency. Race, vitamin D intake, sun exposure, obesity, age, and physical activity all impact individual vitamin D status.