Endurance athletes are very familiar with the various deficiencies that can take affect when increased activity ensues. Both iron deficiencies and calorie deficiencies are notorious and common among endurance athletes. However vitamin D deficiencies are often over looked and seldom do athletes have the proper levels of vitamin D.
So you may be asking why vitamin D is so important. The deficiency is actually very easy to confuse with an iron deficiency because it has similar symptoms. Some of these include fatigue and muscle weakness. Many athletes find themselves not able to train at the same level and longer recovery times. However, a vitamin D deficiency also promotes weaker bones, and interferes with muscle contraction since vitamin D helps to facilitate the movement of calcium to muscles, bones, and other places in the body. Many athletes do not know they have a deficiency until they have a stress fracture caused by the lack of vitamin D.
Blood levels of vitamin D should be at 40 ng/mL or greater. If deficient, this is achieved by adding supplements to the diet or going out in the sun a little more. Daily the average person needs 3,000-5,000 IU in order to maintain normal bodily functions. However, absorbing the vitamin D you do receive is a whole other story.
Many vitamins are best absorbed when taken together, like iron and vitamin C. Vitamin D in turn promotes calcium absorption. But before it can do that, vitamin must be absorbed first. The sun is a source of vitamin D but only a certain frequency of light will be accepted by the body. The sun light at the equator is much different from the sunlight up here in Boone when we talk about how it stimulates our skin's vitamin D production.
Often, any latitude north of Atlanta does not get adequate sun. If you are south of Atlanta, then the time of day can also play a factor in whether or not your skin can produce vitamin D. Just using a sunblock of 15 SPF decreases absorption and vitamin D production by 99%. Lastly, if you naturally have a darker skin color from more melanin, then your vitamin D absorption is decreased as well. More fair skin tones are shown to absorb vitamin D better.
Therefore, if you live in an area where the sun is not in your favor, such as the high country, the next best thing to do is to get your vitamin D from food. However, the absorption of vitamin D is only at 50% without adequate calcium levels. Therefore when eating a vitamin rich food, it is often a good idea to include a calcium rich food with it. Some vitamin D rich foods include fatty fish such as salmon, eggs, fortified cereals, and any fortified beverages such as fortified dairy milk, orange juice, and fortified soy or almond milk. Some vitamin D and calcium combinations include salmon and dark greens or a Greek yogurt based tzatziki sauce. Another may be eggs and some cheese. Any athletes on a strict vegan and vegetarian diet may have trouble reaching proper vitamin D levels. If so, then they may need to take additional supplements and consult their doctor before doing so.