Vitamin D and Black adults: the deficiency paradox and what to actually do

Vitamin D helps your body absorb calcium and keep bones mineralized. Severe, sustained deficiency causes rickets in children and osteomalacia (soft, painful bones) in adults. Your body makes vitamin D in the skin from sunlight, and you also get smaller amounts from food and supplements. The blood test doctors use measures 25-hydroxyvitamin D, written 25(OH)D, which reflects your total stores.

The U.S. Food and Nutrition Board sets these reference points for 25(OH)D: below 12 ng/mL (30 nmol/L) signals deficiency that can cause rickets or osteomalacia; 12 to under 20 ng/mL is generally inadequate; and 20 ng/mL (50 nmol/L) or above is generally adequate for bone and overall health. Those cutoffs were built largely from studies in mostly White populations, which matters for the rest of this story.

Melanin is the pigment that gives skin its color and protects against UV damage. It also reduces the skin's ability to make vitamin D from sunlight. On average, Black adults in the United States therefore show lower total 25(OH)D on blood tests than White adults.

If a lower number simply meant worse bone health, you would expect Black adults to break more bones. The opposite is true. People of African ancestry have lower rates of osteoporosis and bone fracture than White people. That mismatch, a "low" test alongside strong bones, is the paradox, and it points to a problem with the test rather than a hidden epidemic of disease.

The clearest evidence comes from a 2013 study by Camille Powe and colleagues in the New England Journal of Medicine, drawing on 2,085 adults (1,181 Black, 904 White) in the federal HANDLS cohort.

Most circulating vitamin D is bound to a carrier called vitamin D-binding protein and is not immediately usable. Only the small unbound, or "bioavailable," fraction reaches tissues. The study measured both.

• Total 25(OH)D was far lower in Black participants: 15.6 ng/mL versus 25.8 ng/mL in White participants.
• But vitamin D-binding protein was also much lower in Black participants: 168 versus 337 micrograms/mL.
• The result: bioavailable 25(OH)D was essentially the same in both groups, 2.9 versus 3.1 ng/mL, a difference that was not statistically significant.
• Bone mineral density at the femoral neck was higher in Black participants (1.05 versus 0.94 g/cm2).

Two common gene variants in the binding-protein gene (rs7041 and rs4588) explained most of the difference in binding-protein levels between groups. In plain terms: many Black adults run a lower total because they carry less of the protein that locks vitamin D away, leaving a normal amount of the active form free to do its job. The standard total-25(OH)D test does not capture this, so it can label a healthy person "deficient."

Be precise about the limits. The study was cross-sectional, so it cannot prove fracture outcomes; bioavailable D was calculated rather than directly measured for most participants; and later researchers have debated whether the binding-protein assay used can read certain gene variants accurately. The finding is strong and influential, not the final word. It is enough to say the standard test likely overstates deficiency in many Black adults. It is not enough to say binding-protein or bioavailable testing should replace the standard test in everyday care; no guideline endorses that yet.

Genuine, clinically meaningful deficiency is not a borderline lab value. It shows up in the body. In adults, severe deficiency causes osteomalacia: aching bones, bone tenderness, and muscle weakness, sometimes with difficulty climbing stairs or rising from a chair. In children it causes rickets, with soft bones and skeletal deformities.

These are also symptoms many other conditions cause, including thyroid disease, anemia, and depression. Persistent deep fatigue in particular has a long list of causes worth working through with a clinician rather than pinning on a single vitamin. We cover that in why Black women experience chronic fatigue. If you have unexplained bone pain or muscle weakness, that is a reason to be evaluated, and vitamin D testing is appropriate in that workup.

Testing makes sense when there is a reason: symptoms of deficiency, osteoporosis or a fragility fracture, conditions that block fat absorption (such as celiac disease, Crohn's disease, or bariatric surgery), kidney or liver disease, or certain medications.

For healthy adults without those reasons, the guidance has shifted toward less testing. The 2024 Endocrine Society clinical practice guideline suggests against routine 25(OH)D screening in healthy adults, and states specifically that it suggests against routine screening in adults with dark complexion. The U.S. Preventive Services Task Force reached a related conclusion in 2021: there is insufficient evidence to weigh the benefits and harms of screening asymptomatic adults, an "I" statement. Their review did not find that treating low levels in asymptomatic adults reduced fractures, falls, or death.

If you have symptoms or a risk condition, get tested and, if truly deficient, treated. If you are healthy and feel well, a screening number, especially one near the cutoff, rarely changes what you should do.

The recommended dietary allowance is 600 IU per day for adults 19 to 70, and 800 IU per day after 70. The 2024 Endocrine Society guideline supports this for healthy adults under 75 and finds they are unlikely to benefit from more, while suggesting modest empiric supplementation (without testing) for adults 75 and older, pregnant people, children, and adults with prediabetes.

More is not better. The safe upper limit for adults is 4,000 IU per day, and even intakes below that limit may carry adverse effects over time. High-dose vitamin D can raise blood calcium and harm the kidneys.

On the question that drives this search, "should I take vitamin D," the honest answer for a healthy adult is that a standard multivitamin or modest supplement at the recommended dose is reasonable and low-risk, especially with little sun exposure, but it is not a treatment for fatigue or a guarantee against fractures. A large randomized trial settled the fracture question for the general population.

In the VITAL trial, Meryl LeBoff and colleagues randomized 25,871 generally healthy U.S. adults (20.2% Black) to 2,000 IU of vitamin D3 daily or placebo for a median of 5.3 years. Supplementation did not lower the risk of total fractures (hazard ratio 0.98), hip fractures (1.01), or nonvertebral fractures (0.97). Critically, the effect did not differ by race or ethnic group, and starting 25(OH)D level did not change the result.

What the evidence supports: melanin lowers skin vitamin D production; Black adults more often show low total 25(OH)D; many nonetheless have normal bioavailable vitamin D and strong bones; standard cutoffs derived from mostly White populations likely overstate deficiency in Black adults; and routine supplementation does not prevent fractures in healthy adults regardless of race.

What it does not support: that most Black adults are dangerously deficient; that everyone with a "low" number needs treatment; that high-dose supplements improve fatigue, immunity, or bone strength in healthy people; or that binding-protein or bioavailable testing should replace standard testing in routine care.

The practical takeaway: deficiency with symptoms or a risk condition deserves testing and treatment. A borderline number in a healthy person who feels well usually does not. If you want a clinician who will read your labs in context rather than treat a number, you can find a provider through our directory.