Gabriella Rao, RD

This time I’m switching things up from minerals to talk about a very important vitamin: vitamin D! Vitamin D is a fat-soluble vitamin and hormone that the body can synthesize from exposure to sunlight. It’s very important for general health, and also has a few very important functions that promote health and longevity in endurance sport. 

Functions of vitamin D:

• Promotes absorption of calcium, magnesium, and phosphorus
• Bone health
• Mood regulation
• Associated with reduced risk of pretty much every chronic disease
• Muscle recovery
• Reduces inflammation throughout the body

The RDA for vitamin D is 600-800 IU for adults. Vitamin D deficiency can arise from too little sunlight exposure, as well as depletion of stores (which can occur more often in endurance athletes). If you live above the 37th parallel (San Francisco or north) as most of us likely do, it’s very possible that you will require vitamin D supplementation, especially through the winter months. 

Symptoms of deficiency:

• Muscle weakness or pain
• Fatigue
• Mood changes
• Bone injuries
• Frequent illness

Sources of vitamin D:

• As aforementioned, sunlight exposure is the best way to trigger synthesis of vitamin D. Ten to 30 minutes a day of midday sun several times per week is recommended.
• Fatty fish (salmon, mackerel, sardines)
• Beef liver
• Egg yolk
• Cheese
• Fortified milks
• Mushrooms
• Tofu

Assessment of vitamin D:

• Serum vitamin D [the lab itself is called 25(OH)D] values of < 50 nmol/L indicate insufficiency, while < 30 nmol/L indicates deficiency

Supplementation: recommend working with PCP or RD prior to starting supplementation!

• Vitamin D3 supplements (vs D2) have been shown to be more effective in increasing and maintaining vitamin D levels
• For those with severe deficiency, high-dose supplementation of 50,000 IU weekly or 6,000 IU daily for 6-8 weeks is recommended. After correction, the maintenance dose is 2,000 IU daily.
• For those with adequate vitamin D but who live in not-sunny places, a daily dose of 400-1,000 IU is likely adequate to maintain stores. 
• Vitamin D is a fat-soluble vitamin, and can be toxic in high levels!
  • The Tolerable Upper Intake Level (UL) for vitamin D is 4,000 IU daily. 
• Ensure the brand you choose is third-party tested (from a company like NSF, Informed Sport, or ConsumerLabs, etc.), so that you can be confident that the supplement doesn’t contain any contaminates and provides the amount of vitamin D listed on the label
  • Third-party tested brands include: Nordic Naturals, Thorne, NOW foods, Momentous, Garden of Life