The Lowdown on Vitamin D

Look at all the great gear available for training. Wool hats, fleece gloves and wicking base layers are fantastic items to have. That is, until we consider sunlight. They keep us covered and we miss out on receiving beneficial rays of the sun. Since the suns rays do not contact our skin we are unable to produce vitamin D.

Vitamin D is produced when the UVB rays of the sun are absorbed by our skin, particularly our face, hands, arms, and back. In the Northeast, our latitude prevents us from producing vitamin D between November and February. As we approach the spring and warmer weather, we should consider reducing some layers to get some sun exposure. Sunlight during the midday offers the best angle to start the process of vitamin D production.

Vitamin D acts like a switch to turn on cells that are important for the immune system, cardiovascular system, muscular function, bone health, inflammatory responses and mental state. Symptoms of vitamin D deficiency are silent and easily overlooked. Muscle and joint pain and fatigue could be a sign of over training or related to vitamin D deficiency. The only way to truly know is to have a 25 (OH)D blood test performed.

Certain factors limit us from having optimal levels of vitamin D. A lifestyle with limited exposure to the outdoors is problematic. Indoor treadmill running does not allow the body to produce vitamin D. Also by running early in the morning or later in the evening, the angle of the suns rays is such that you are not making vitamin D. Doesn't that describe most of us? We run before or after work and miss the opportunity to run when the sun allows us to produce vitamin D. The healing rays of sunlight cannot penetrate glass, when you are at home, work, or in your car. Having a higher percent body fat is a challenge to vitamin D production. Sunscreen use also hinders absorption of sunlight. The chemicals in sunscreen are designed to protect our body from skin cancer. However, these same chemicals also prevent us from absorbing sun rays necessary for producing vitamin D. The recommendation is to spend about 15 - 20 minutes in the midday sun most days of the week and then apply sunscreen. Those with darker skin tones need more time in the sun than those with a fairer complexion. The body produces 10,000 IUs (international units) from 20 minutes of sun exposure.

Food provides us with only small amounts and limited sources of our necessary D levels. Top on the list is cod liver oil. One tablespoon provides 1,300 IUs. The newly updated RDA (recommended daily allowance) for individuals 9 - 70 years old is 600 IU. The upper level for that age group shifted from 2,000 IU up to 4,000 IU.

Food Sources of Vitamin D


Serving Size

IUs per serving

Cod Liver Oil1 Tablespoon


Wild Sockeye Salmon3.5 oz


Mackerel3 oz


Shrimp3.5 oz


Milk (Vitamin D fortified)1 cup


Orange Juice (Vitamin D fortified)1 cup


Cereal (fortified with 10% of the DV for Vitamin D)0.75 - 1 cup


Butter2 Tablespoon


Egg (Vitamin D is in the yolk)1 whole


Source: The world's healthiest foods

To get the required vitamin D levels and to boost a body that is deficient, supplementation may be necessary. Results from a blood test will assist your healthcare provider to determine if supplementation is appropriate for you. It is common and safe to start with 1,000 - 2,000 IU/day. Vitamin D supplements are sold in two forms, natural vitamin D3 or synthetic vitamin D2.

As we approach spring, try to take advantage of warmer weather with better angles of the sun to help your body produce vitamin D. Twenty minutes of sun exposure a day could help prevent a deficiency in vitamin D. Supplementation gives you added security by boosting those levels. If vitamin D is truly the vitamin that prevents certain disease you’ll be covered.