---
title: Vitamin D Dosing in Clinical Trials
description: As reviewed in a recent Biotics Research Forum, an abstract recently presented at the American Heart Association’s Scientific Sessions suggests that personalized dosing of vitamin D may reduce the risk of heart attacks among people with cardiovascular disease. While not yet peer-reviewed, what is notable in this trial (in addition to the substantial risk reduction) is that a fixed dose of vitamin D was not used. Rather, the TARGET-D trial personalized doses to achieve specific blood levels of 25-OH vitamin D (25-OHD). Other trials suggest there may also be advantages to daily dosing rather than large boluses, genetic and other modifiers, etc., meriting a general review of the evidence related to vitamin D dosing.
---

[Biotics Research Blog ](https://blog.bioticsresearch.com)

# [Vitamin D Dosing in Clinical Trials](https://blog.bioticsresearch.com/vitamin-d-dosing-in-clinical-trials)

 Written by [The Biotics Education Team](https://blog.bioticsresearch.com/author/the-biotics-education-team) | Jan 6, 2026 2:30:06 PM

As reviewed in a recent [Biotics Research Forum](https://info.bioticsresearch.com/researchforum/vitamin-d-heart-attack-risk), an [abstract](https://newsroom.heart.org/news/heart-attack-risk-halved-in-adults-with-heart-disease-taking-tailored-vitamin-d-doses) recently presented at the American Heart Association’s Scientific Sessions suggests that personalized dosing of vitamin D may reduce the risk of heart attacks among people with cardiovascular disease. While not yet peer-reviewed, what is notable in this trial (in addition to the substantial risk reduction) is that a fixed dose of vitamin D was not used. Rather, the TARGET-D trial personalized doses to achieve specific blood levels of 25-OH vitamin D (25-OHD). Other trials suggest there may also be advantages to daily dosing rather than large boluses, genetic and other modifiers, etc., meriting a general review of the evidence related to vitamin D dosing.  

Several studies suggest that daily to weekly supplementation has clinical benefits, while large monthly or annual dosing either has no benefit or carries some degree of harm. For example, a 2025 systematic review and meta-analysis [published in](https://pubmed.ncbi.nlm.nih.gov/39993397/) *The Lancet, Diabetes & Endocrinology* found no overall benefit of vitamin D supplementation compared to placebo for the risk of acute respiratory infections (ARI). This analysis comprised 46 randomized and controlled clinical trials, involving over 64,000 participants. A closer examination of the results revealed statistically significant protection with vitamin D for specific subsets. Regarding dosing frequency, a daily dose was associated with a 16% lower risk of ARI, whereas no protective benefit was observed for either weekly or monthly dosing. Additionally, dosing of 400-1000 IU was associated with a 30% lower risk for ARI, while higher and lower doses were not associated with benefit (none were targeted to a specific 25-OHD level).  

High boluses of vitamin D have also been linked to harm in some studies. *JAMA*, for example, [published the results](https://pubmed.ncbi.nlm.nih.gov/20460620/) of a double-blind clinical trial that found that among older community-dwelling women, an annual dose of 500,000 IU cholecalciferol (D3) given annually for 3 to 5 years was associated with an increase in both falls and fractures. Similarly, *JAMA Internal Medicine* [published the results](https://pubmed.ncbi.nlm.nih.gov/26747333/) of a one-year clinical trial which found that compared to monthly dosing of 24,000 IU vitamin D3, a higher dose of 60,000 D3 did not improve lower extremity function, and was associated with an increase in fall risk (with similar results for a group receiving 24,000 IU D3 in addition to 300 μg of calcifediol (active D, i.e., 25-OH vitamin D). When combined with calcium, *daily* doses of vitamin D [have been shown](https://pubmed.ncbi.nlm.nih.gov/32846760/) to lower [fracture rates](https://pubmed.ncbi.nlm.nih.gov/35504603/) and [fall incidence](https://pubmed.ncbi.nlm.nih.gov/38698349/) in several ([but not all](https://pubmed.ncbi.nlm.nih.gov/35939577/)) clinical trials, without evidence of harm. 

There may be other modifiers of vitamin D’s effectiveness. Genetic polymorphisms are likely to play a role; for example, in 2023, *JAMA Oncology* published [a secondary analysis](https://pubmed.ncbi.nlm.nih.gov/36701139/) of a randomized and controlled trial, which suggests that people with variants in the vitamin D binding protein (DBP) gene are more likely to benefit from vitamin D supplementation. In this trial, over 1,600 people who were recently diagnosed with a colorectal adenoma were given either vitamin D, calcium, both, or a placebo and followed for 3-5 years. People with at least one A allele in the rs4588 SNP (coding for the DBP2 isoform) had a lower risk of recurrence with either calcium or vitamin D supplementation, with the lowest risk observed for the combination (24% lower than placebo). Additionally, this risk was 43% lower among people with two A alleles (homozygotes) in this SNP, while people with the CC genotype had no statistical benefit with either supplement. DPB is a vitamin D carrier protein, and the DBP2 isoform is associated with lower levels of 25-OHD. [Additional data](https://pubmed.ncbi.nlm.nih.gov/27978548/) from the same trial also found that vitamin D effectiveness was influenced by other genes, such as the vitamin D receptor gene.  

BMI-based effectiveness of vitamin D supplementation may also be worth evaluating. In 2023, *JAMA Network Open* [published an analysis](https://pubmed.ncbi.nlm.nih.gov/36648947/) from VITAL (Vitamin D and Omega-3 Trial), which found that the effects of vitamin D supplementation on serum vitamin D-related biomarkers (including free and bioavailable vitamin D,  25-OHD, etc.) were blunted among people with overweight or obesity. Varying effects on 25-OHD levels with body weight [have been observed](https://pubmed.ncbi.nlm.nih.gov/23246640/) previously, and a Mendelian randomization [published in](https://pubmed.ncbi.nlm.nih.gov/23393431/) *PLoS One* suggests that a higher BMI leads to a lower 25-OHD, with the reverse phenomenon (a lower 25-OHD leading to a higher BMI) is likely to only be a small effect. An analysis of over 17,000 healthy volunteers also [published in](https://pubmed.ncbi.nlm.nih.gov/25372709/) *PLoS One* suggests that vitamin D supplementation should be 2-3 times higher for people with obesity and 1.5 times higher for people with overweight.  

While there have been many disappointing trials evaluating vitamin D supplementation, it remains difficult to generalize. Were the doses chosen in the trials appropriate and reflective of differences in BMI and/or genetic variants? Were the doses targeted to a specific 25-OHD or a fixed dose, with the latter likely to have inconsistent effects on the target population? Hopefully, more trials like the TARGET-D study are implemented, and include an analysis of some of the variables related to vitamin D efficacy. 

[View full post](https://blog.bioticsresearch.com/vitamin-d-dosing-in-clinical-trials)

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