Vitamin D deficiency is epidemic. If you work indoors, live north of Atlanta, or have darker skin, you probably need to supplement. The tricky part: most products don't contain enough.
D3 vs D2
Vitamin D3 (Cholecalciferol) - What your skin makes from sunlight - More effective at raising blood levels - Stays in your system longer - From animal sources (lanolin, fish) or lichen (vegan D3)
Vitamin D2 (Ergocalciferol) - From fungi/plants - Less effective per dose - Clears from body faster - Sometimes prescribed in high doses
Bottom line: Choose D3 unless you need a vegan source (lichen-derived D3 exists now)
Where to Find Vitamin D
Standalone D3 - Best option - 1000-10000 IU per serving - Often combined with K2 (helps direct calcium to bones) - Liquid drops allow flexible dosing
Multivitamins - Usually underdosed - Most contain only 400-800 IU - The RDA (600-800 IU) is probably too low - Need additional D3 for most people
D3 + K2 combos - Increasingly popular - K2 helps calcium go to bones, not arteries - Good synergy - MK-7 form of K2 preferred
Fish oil - Some contain added D3 - 1000 IU typical - Check if included
Calcium supplements - Sometimes include D3 - Usually 400-600 IU - Not enough on its own
How Much Do You Need
Official RDA: 600-800 IU
What researchers often recommend: 2000-5000 IU daily
Factors increasing your need: - Darker skin - Northern latitude - Indoor lifestyle - Obesity - Age over 60
Get tested: 25-hydroxy vitamin D blood test - Under 30 ng/mL: Deficient - 40-60 ng/mL: Optimal for most
Take with fat for proper absorption
Upper limit: 10,000 IU daily long-term (higher doses require monitoring)