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Strong evidenceGeneral health

Vitamin D3

Essential for bone health, muscle function, and immunity. Supplementation is clearly beneficial for people who are deficient — a very common condition worldwide.

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What the science says

  • Correcting deficiency and bone health Strong evidence

    Vitamin D deficiency impairs bone mineralization (osteomalacia, rickets), and supplementation corrects deficiency effectively. Together with calcium, it reduces fracture risk in older adults with low levels.

  • Immune support Moderate evidence

    A meta-analysis of randomized trials suggests a modest reduction in the risk of acute respiratory infections, with the greatest benefit in people with marked deficiency.

  • Preventing chronic disease in people with normal levels Limited evidence

    Large trials (such as VITAL) showed no reduction in cardiovascular events or cancer with supplementation in people who are not deficient.

Dosage & safety

Studied dose1,000–2,000 IU/day is common for maintenance; deficiency requires higher doses under medical supervision with blood testing (25-OH-vitamin D).
SafetySafe at usual doses. Very high doses over long periods can cause hypercalcemia. It is fat-soluble: taking it with a meal improves absorption.

How to take it

TimingTiming does not matter; a weekly dose works as well as a daily one for maintenance.
With food?With the largest meal of the day containing fat — this measurably increases absorption of a fat-soluble vitamin.
Worth knowingTest 25-OH vitamin D rather than guessing: the right dose for someone deficient and someone already replete differs several-fold.

Interactions

With medications

  • thiazide diuretics

    Thiazides reduce urinary calcium excretion, so combined with vitamin D (especially plus calcium) they raise the risk of hypercalcaemia. have calcium checked if you take both long-term

  • digoxin

    If vitamin D raises calcium, digoxin toxicity and arrhythmia risk increase. do not use high doses without medical supervision

  • orlistat, cholestyramine and other bile acid sequestrants

    They bind fat and cut absorption of fat-soluble vitamins including D. separate by at least 4 hours and expect to need a higher dose

With other supplements

  • calcium

    Vitamin D increases calcium absorption, so high doses of both together carry the real hypercalcaemia and kidney stone risk, not either one alone. do not stack high doses of both without a blood calcium check

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Is vitamin D worth taking?

Vitamin D is clearly worth taking if you are deficient, which is common worldwide — the evidence for correcting deficiency and, with calcium, reducing fractures in older adults is strong. In people with normal levels, large trials such as VITAL showed vitamin D did not reduce heart disease or cancer.

How much vitamin D3 per day?

For maintenance, 1,000–2,000 IU/day of vitamin D3 is common. Deficiency needs higher doses under medical supervision, so test your 25-OH vitamin D rather than guessing.

When should I take vitamin D, and with food?

Take vitamin D with the largest meal of the day containing fat, which measurably increases absorption. Time of day does not matter, and a weekly vitamin D dose works as well as a daily one for maintenance.

Does vitamin D help prevent colds and flu?

Moderately — a meta-analysis of randomized trials suggests vitamin D modestly reduces acute respiratory infections, with the greatest benefit in people who are markedly deficient. The evidence for this use is moderate, not strong.

Scientific references

Where to buy

California Gold Nutrition, Vitamin D3, 125 mcg (5,000 IU), 90 Fish Gelatin Softgels

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