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ingestible · for immune support

Vitamin D3 (cholecalciferol)

Reviewed by the Nimbera editorial team · Last updated May 2026

Martineau et al. (2017, BMJ, PMID 28202713) conducted a meta-analysis of individual participant data from 25 RCTs (n=10,933). Daily or weekly vitamin D supplementation reduced the odds of acute respiratory infection (aOR 0.81, 95% CI 0.72-0.91). Individuals with severe baseline deficiency showed the greatest benefit (aOR 0.30, 95% CI 0.17-0.53).$8-$20 for a 3-month supply at 1,000-2,000 IU/day.

How to use

Take 1,000-2,000 IU (25-50 mcg) of vitamin D3 daily with a fat-containing meal to aid absorption. Have serum 25(OH)D tested to confirm deficiency before high-dose supplementation.

How it works

Vitamin D receptors are expressed on most immune cells. Adequate vitamin D upregulates antimicrobial peptides (cathelicidin, defensins) and modulates the inflammatory response, helping the innate immune system clear pathogens without excessive tissue damage.

Where to buy

Widely available at pharmacies and supermarkets. Gel capsules or oil-based softgels absorb better than dry tablets.

Typical cost: $8-$20 for a 3-month supply at 1,000-2,000 IU/day.

Safety notes

The tolerable upper intake for adults is 4,000 IU/day. Doses above this should only be taken under medical supervision, as vitamin D toxicity (hypercalcaemia) is possible. People with granulomatous diseases or certain lymphomas should not supplement without physician approval.

Drug & supplement interactions

  • Always tell your doctor or pharmacist about any supplements you take.
  • Interactions can occur with prescription medications, blood thinners, and immunosuppressants.
  • Herbal remedies can affect how the body absorbs or metabolises drugs.
  • Check drugs.com interactions checker before starting.

Clinical source

Martineau AR et al., Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data, BMJ, 2017

This information is compiled from primary clinical literature and is for informational purposes only. It is not a substitute for professional medical advice. Read our full disclaimer.