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Estimate vitamin D from sun, food and supplements — see total IU, % of RDA and safe upper limit.
Estimate vitamin D from sun, food and supplements — see total IU, % of RDA and safe upper limit.
Enter values above and click Calculate — results will appear here with the formula explained.
Midday sun on arms and legs synthesizes roughly 8–25 IU per minute for fair skin — highly variable with latitude, season, time of day, exposed area, skin tone and sunscreen. Food contributes modestly (salmon ~450 IU per serving, fortified milk ~120 IU per cup, eggs ~40 IU each). Supplements fill the gap with labeled precision sun and food lack.
RDA is 600 IU daily for adults 19–70 and 800 IU for 71+, with a tolerable upper limit of 4,000 IU. These cover bone health for 97–98% of the population; athletes, the obese (vitamin D sequesters in fat) and the chronically ill often need clinically guided higher intakes — this is general information, not medical advice, and blood testing (25-OH-D) is the only personal dosing basis.
Season and geography dominate real status: above ~37° latitude, winter UVB is insufficient for synthesis regardless of time outdoors (Boston gets effectively zero November–February); darker skin needs 2–3× longer exposure for equivalent IU; sunscreen SPF 30+ cuts synthesis ~90%+ (correctly — never trade burns for IU); aging skin synthesizes less efficiently; and glass blocks UVB entirely, so sunny windows don't count.
D2 versus D3: cholecalciferol (D3, animal/lanolin-derived or lichen vegan) raises blood levels more effectively than ergocalciferol (D2, plant/fungal). Take D3 with fat-containing meals for absorption (it's fat-soluble), and note magnesium and K2 cofactor roles often cited in protocols — discuss combos with a clinician rather than stacking blindly.
Deficiency signs are nonspecific — fatigue, bone pain, muscle weakness, frequent illness — which is why testing beats symptoms: 25-OH-D below 20 ng/mL is deficient, 20–30 insufficient, 30–50 sufficient for most, with toxicity concerns above 100–150. Re-test 8–12 weeks after protocol changes; levels move slowly.
Overdose is real but hard via sun (skin self-limits) — risk comes from chronic supplement excess above 4,000 IU/day, causing hypercalcemia: nausea, confusion, kidney stones. Food alone essentially never overdoses. Keep total (sun estimate + food + supplement) under the upper limit here, and involve a clinician above it.
Estimate vitamin D from sun, food and supplements — see total IU, % of RDA and safe upper limit. Formula: Total = sun*~8 IU per minute (midday, fair skin, arms/legs) + food + supplement.
Midday sun on arms and legs synthesizes roughly 8–25 IU per minute for fair skin — highly variable with latitude, season, time of day, exposed area, skin tone and sunscreen. Food contributes modestly (salmon ~450 IU per serving, fortified milk ~120 IU per cup, eggs ~40 IU each). Supplements fill the gap with labeled precision sun and food lack.
RDA is 600 IU daily for adults 19–70 and 800 IU for 71+, with a tolerable upper limit of 4,000 IU. These cover bone health for 97–98% of the population; athletes, the obese (vitamin D sequesters in fat) and the chronically ill often need clinically guided higher intakes — this is general information, not medical advice, and blood testing (25-OH-D) is the only personal dosing basis.
Season and geography dominate real status: above ~37° latitude, winter UVB is insufficient for synthesis regardless of time outdoors (Boston gets effectively zero November–February); darker skin needs 2–3× longer exposure for equivalent IU; sunscreen SPF 30+ cuts synthesis ~90%+ (correctly — never trade burns for IU); aging skin synthesizes less efficiently; and glass blocks UVB entirely, so sunny windows don't count.
D2 versus D3: cholecalciferol (D3, animal/lanolin-derived or lichen vegan) raises blood levels more effectively than ergocalciferol (D2, plant/fungal). Take D3 with fat-containing meals for absorption (it's fat-soluble), and note magnesium and K2 cofactor roles often cited in protocols — discuss combos with a clinician rather than stacking blindly.
Deficiency signs are nonspecific — fatigue, bone pain, muscle weakness, frequent illness — which is why testing beats symptoms: 25-OH-D below 20 ng/mL is deficient, 20–30 insufficient, 30–50 sufficient for most, with toxicity concerns above 100–150. Re-test 8–12 weeks after protocol changes; levels move slowly.
Overdose is real but hard via sun (skin self-limits) — risk comes from chronic supplement excess above 4,000 IU/day, causing hypercalcemia: nausea, confusion, kidney stones. Food alone essentially never overdoses. Keep total (sun estimate + food + supplement) under the upper limit here, and involve a clinician above it.
With 15 min midday sun (~120 IU) + 200 IU food + 1,000 IU supplement = ~1,320 IU, 220% of the 600 IU RDA and safely under the 4,000 IU upper limit. Same person in Boston January gets ~0 from sun — total falls to 1,200 IU, still adequate only because of the supplement.
Last reviewed: September 2026 · Report an error