Key facts
- Supports bone, immune, and muscle function.
- Made in the skin from sun exposure.
- Deficiency is common, especially in winter.
- Often worth supplementing if sun exposure is low.
Vitamin D acts more like a hormone than a typical vitamin, playing roles in bone health (via calcium absorption), immune function, and muscle performance. Your body produces it when skin is exposed to sunlight, with smaller amounts coming from foods like fatty fish and fortified products.
Because of limited sun exposure — especially in winter, at higher latitudes, or with indoor lifestyles — deficiency is common. Low vitamin D can affect mood, immunity, and possibly strength. Supplementing is a simple, low-cost fix when sun exposure is inadequate; testing your levels can guide whether and how much you need.
Frequently asked questions
Should I supplement vitamin D?
If your sun exposure is limited (winter, high latitude, mostly indoors), supplementing is often worthwhile. Testing your blood levels helps determine whether and how much you need.
Why is vitamin D important for fitness?
It supports bone health, immune function, and muscle performance. Low levels are common and can affect strength, recovery, and overall health.
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