Vitamin D is a fat-soluble vitamin necessary for the absorption of calcium. Therefore, vitamin D is essential for bone health as well as immune function, lowering risk or chronic disease, reduction in inflammation, and brain function and mood. Vitamin D deficiency has also been linked to depression (2). Vitamin D supplementation is by no means a cure-all for depression, but evidence is showing a correlation. Therapeutic supplementation of vitamin D (100,000 IUs) improved depression more than sun lamps in one population.
There are two sources of vitamin D - the food we eat and sunshine. Unfortunately, sufficient vitamin D it is difficult to obtain from either of these two sources. Very few foods naturally contain vitamin D although some are fortified (i.e. milk). Absorption of vitamin D from the sun depends on relative distance to the sun. Even 40% of Louisiana distance runners tested had low serum (blood) vitamin D levels (1). Darker skin tones as well as sunscreen also prevent absorption.
600 - 1000 IU of vitamin D3 (the active form of vitamin D) is recommended per day, especially during the darker months of winter. You can also bump up intake of fortified dairy (milk and yogurt), salmon and tuna (canned with bones has even more), sardines, mushrooms, and containing smaller amounts, eggs.
Symptoms of vitamin D deficiency may be hard for us to notice - they include bone and muscle pain and weakness. Not sure about the rest of you, but that is a daily occurence for me. Ask your doctor to check you vitamin D levels - 25 (OH) D specifically - next time you have a physical. Not scheduled for a physical? Not a bad idea to give the doc a call. While you are in, have them look at your iron before ramping up training for the spring season.
(1) Willis. Int'l J Sports Nutr 2008; 18: 204-225.
(2) Hoogendijik, WJ et al. Depression is associated with decreased 25-hydroxyvitamin D and increased parathyroid hormone levels in older adults. Arch Gen Psychiatry. 2008; 65(5): 508-512.