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Should you get your vitamin D level tested, and what number should you aim for?

What the experts say

Rhonda PatrickPhD · biomedical scientist and science communicator, founder of FoundMyFitness

Measure it rather than guessing at a dose, and treat 40 to 60 ng/mL as the range to aim at.

What it rests onHer stated reasoning is that the existing recommended levels were derived from vitamin D's role in bone metabolism and it is unknown whether they are adequate for immune function, so the storage form should be measured and the number used as the input. On the range, she describes a meta-analysis of studies from the 1960s to 2013 relating all-cause mortality to blood levels, and says the lowest mortality sat 'somewhere between 40 to 60, or 70', calling it a sweet spot. She raises the Institute of Medicine's 4,000 IU upper tolerable intake in the same passage, and her own site's vitamin D article reports the IOM and Endocrine Society thresholds without issuing a dose in her voice.

Source: foundmyfitness.com ↗
Andrea LovePhD · immunologist and microbiologist

Do not order population-based screening for vitamin D, and do not supplement for general health. Deficiency is far less common than believed because the threshold was set too high.

What it rests onShe argues from high-quality randomised trials that supplementation does not prevent respiratory illness, cardiovascular disease, cancer or fractures and does not reduce mortality, and cites USPSTF, the National Academy of Medicine, the ABIM Foundation and the American Society for Clinical Pathology against population screening, on the grounds that the test is medically unnecessary and manufactures a belief in widespread deficiency. Read in context, she is not against all testing or all supplementation: she names exceptions where supplementation is beneficial, including at least partially breastfed newborns and people with conditions affecting absorption or storage such as Crohn's disease, cystic fibrosis, coeliac disease, certain liver and kidney diseases, and after gastric bypass. Her threshold is the Institute of Medicine's 20 ng/mL.

Source: news.immunologic.org ↗

Overview

Love is addressing asymptomatic general adults with no clinical reason to test, and explicitly exempts newborns and people with malabsorption or storage conditions. Patrick is addressing adults who want to optimise immune function and long-term risk, and her mortality evidence is observational association across cohorts rather than trial outcome.

The two sides route the same asymptomatic adult in opposite directions, which is what makes this a real disagreement rather than a difference of emphasis.

Where they agree

Both hold that vitamin D toxicity is real and dose-dependent, both cite the Institute of Medicine's 4,000 IU upper tolerable intake, and both accept that specific clinical populations benefit from supplementation. Patrick's own site reports the IOM thresholds Love argues from, so neither side disputes the other's numbers, only what to do with them.

What would settle it

A randomised trial powered on hard outcomes that assigns people to a 40 to 60 ng/mL target rather than to a fixed dose. Every trial in Love's evidence base assigns a dose, which is precisely the design Patrick's position predicts will null out, and no trial has tested the target-driven version. Failing that, a mortality analysis in which the 40 to 60 ng/mL association survives adjustment for the confounders that plausibly produce it.

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