The Endocrine Society suggests against extra vitamin D for healthy adults under 75

The Endocrine Society's 2024 clinical practice guideline suggests against taking vitamin D above the current Dietary Reference Intakes to lower disease risk in healthy adults younger than 75, and suggests against routine blood testing for 25-hydroxyvitamin D in every population it considered [s1]. Its stated reason for the testing recommendation is that the panel found no clinical trial evidence supporting screening in the general population, and no clear evidence defining what target level would even be aimed for [s1].

That is a narrower conclusion than either side of the vitamin D argument usually reports, and it comes with specific exceptions.

What the guideline does and does not recommend

The panel was assembled to answer a defined question: whether empiric vitamin D — which it defines as intake exceeding the Dietary Reference Intakes and taken without testing blood levels — lowers disease risk in people who have no established indication for vitamin D treatment [s1]. It prioritised randomised placebo-controlled trials in general populations and used GRADE methodology to grade the certainty of the evidence behind each of 14 prioritised clinical questions [s1].

Four groups came out with a suggestion in favour. The panel suggests empiric vitamin D for children and adolescents aged 1 to 18, to prevent nutritional rickets and for its potential to lower the risk of respiratory tract infections; for adults aged 75 and older, for its potential to lower mortality; in pregnancy, for its potential to lower the risk of pre-eclampsia, intra-uterine mortality, preterm birth, small-for-gestational-age birth and neonatal mortality; and in high-risk prediabetes, for its potential to reduce progression to diabetes [s1].

Everyone else falls under the negative recommendation. The panel suggests against empiric supplementation above the current DRI to lower disease risk in healthy adults younger than 75 [s1].

One further limitation is stated plainly by the panel and is routinely dropped when these recommendations are summarised: because doses across the included trials varied considerably, and many participants were permitted to keep taking their own vitamin D–containing supplements, the optimal dose for empiric supplementation remains unclear even in the groups where the panel does suggest it [s1]. For non-pregnant people over 50 for whom vitamin D is indicated, the panel suggests daily administration rather than intermittent high doses [s1]. The guideline is explicit that it was not designed to replace the existing Dietary Reference Intakes, and does not apply to people who already have an established indication for treatment or testing [s1].

The trial the guideline had to weigh

The largest single piece of evidence is VITAL, a nationwide randomised, placebo-controlled trial in the United States with a two-by-two factorial design, testing vitamin D3 at 2,000 IU per day and marine n-3 fatty acids at 1 g per day for the prevention of cancer and cardiovascular disease in men aged 50 and over and women aged 55 and over [s2]. It randomised 25,871 participants, including 5,106 Black participants [s2].

Over a median 5.3 years of follow-up, vitamin D was not associated with a lower risk of either primary endpoint. Cancer was diagnosed in 1,617 participants — 793 on vitamin D and 824 on placebo, a hazard ratio of 0.96 (95% CI 0.88 to 1.06, P=0.47) [s2]. A major cardiovascular event occurred in 805 participants, 396 on vitamin D and 409 on placebo, a hazard ratio of 0.97 (95% CI 0.85 to 1.12, P=0.69) [s2]. Across 978 deaths from any cause the hazard ratio was 0.99 (95% CI 0.87 to 1.12) [s2]. No excess of hypercalcaemia or other adverse events was identified [s2].

Secondary endpoints were similarly flat, with one number that gets quoted selectively: death from cancer, across 341 deaths, gave a hazard ratio of 0.83 (95% CI 0.67 to 1.02) [s2]. The confidence interval crosses 1, and it was one of many secondary analyses.

Bone, the use most people assume is settled

The most common lay justification for a vitamin D supplement is bone health. A VITAL ancillary study tested exactly that in 25,871 participants who were not recruited on the basis of vitamin D deficiency, low bone mass or osteoporosis [s3]. Over a median 5.3 years, 1,991 incident fractures were confirmed in 1,551 participants [s3].

Vitamin D3 had no significant effect on total fractures — 769 of 12,927 in the vitamin D group against 782 of 12,944 on placebo, a hazard ratio of 0.98 (95% CI 0.89 to 1.08, P=0.70) — nor on non-vertebral fractures (hazard ratio 0.97, 95% CI 0.87 to 1.07) or hip fractures (hazard ratio 1.01, 95% CI 0.70 to 1.47) [s3]. The result did not change by age, sex, race or ethnic group, body-mass index, or baseline serum 25-hydroxyvitamin D [s3].

That last clause is the important one. The trial did not find a subgroup with low baseline levels in whom supplementation worked; it found no modification of the treatment effect by baseline vitamin D status at all [s3].

What remains genuinely open

None of this addresses people with an established indication — diagnosed deficiency, malabsorption, chronic kidney disease, osteoporosis under treatment — who were outside the scope of both the guideline and the trials [s1] [s3]. Nor does it settle the four populations where the Endocrine Society panel did suggest supplementation, since in each of those the panel's confidence rests on "potential" benefit rather than a definitive result, and the dose question is unresolved [s1]. The panel itself calls for further research to determine optimal 25-hydroxyvitamin D levels for specific health benefits [s1].

Whether any individual should take a supplement, at what dose, or be tested, is a clinical question that depends on circumstances these trials deliberately excluded. This article describes what the trials and the guideline found; it is not advice about either.