VitaminNo.011

Vitamin D3

Bone health, calcium absorption, immune function.

Typical / RDA600–800 IU

Upper limit4,000 IU

EvidenceStrong

How to take it

Timing With breakfastFood With fatForm D3 (cholecalciferol)

What to know

Fat-soluble — take with a meal containing fat. Deficiency is common in indoor workers, darker skin, and limited sun. Strong evidence for correcting measured deficiency.

Interactions & cautions

Works with magnesium (activation cofactor) and vitamin K2.
Excess over long periods raises blood calcium — stay under the UL.

Often worth it

Indoor worker or rarely eat oily fish? A likely candidate.

Questions people ask about vitamin d3

Vitamin K2 and Vitamin D3: Interaction, Absorption, and SafetyVitamin D3 and K2 are safe and synergistic. D3 aids calcium absorption, while K2 directs it to bones. Learn optimal timing and doses.
Multivitamin vs Omega-3: Do You Need Both?Mostly, but carefully check your multivitamin label. Many already contain Vitamin D, which can lead to stacking if you take a separate D supplement. Omega-3 is less likely to be duplicated.
Can You Take Too Much Vitamin D3? Side Effects and Daily LimitsYes, taking too much Vitamin D3 can lead to side effects, primarily by raising blood calcium. The upper limit for adults is 4,000 IU daily.
Calcium and Vitamin D: Why You Need Both for Bone HealthCalcium needs vitamin D for proper absorption. They are often taken together for bone health, with adults needing 1,000–1,200 mg calcium and 600–800 IU vitamin D daily.

See how this fits your full stack →

Reference values: NIH Office of Dietary Supplements, adult general population. Educational information only — not medical advice. Confirm with a healthcare professional.