Does melanin block vitamin D?

In the skin, yes. Eumelanin absorbs UVB photons before they reach the 7-dehydrocholesterol that becomes previtamin D3, so the same UV dose makes less vitamin D in darker skin. Melanin has no effect on vitamin D from food or supplements.

Does dark skin absorb less vitamin D?

No. The gut takes up vitamin D from food and supplements the same way in every skin type. Dark skin makes less vitamin D per minute of sun; it does not absorb less.

Can dark skin get sunburned?

Yes. Type VI skin needs roughly eight times the UV dose of type I to redden, which at UV 9 is a matter of hours rather than minutes, not never. Sunburn is an adaptive inflammatory response that the skin mounts to remove stressed cells and thicken its barrier (Vind 2024), and it runs in every skin type.

Is vitamin D deficiency overdiagnosed in Black people?

It is an open question. Powe 2013 found lower vitamin D binding protein in Black Americans, which would leave the free fraction similar despite a lower total 25(OH)D, and Nielson 2016 traced much of that difference to the assay used. The 25(OH)D test is still the only practical measure, and a level under 20 ng/mL is worth acting on whatever your skin color.

Is the UV index a measurement of sunlight?

No. The UV index is a sunburn-weighted score: solar UV weighted by how efficiently each wavelength reddens skin, then summed. UVB dominates that weighting and UVA barely registers, so the index is a proxy for burn risk and says little about the rest of the light. Two moments with the same index can carry very different spectra.

How does Sunlight is Life calculate UV?

It runs a solar physics engine that models the actual sunlight reaching your coordinates, not the nearest city, and shows the UVA and UVB you are receiving separately, updating while the app is open. Your Fitzpatrick type does not change that number; it changes the safe-exposure time and vitamin D estimate built on it. It is still a model, not a measurement of your sky.

How Much Sun Do People With Dark Skin Need for Vitamin D?

Peter CowanSeptember 16, 20265 min read

Three to eight times more than fair skin needs at the same UV index. Melanin absorbs UVB before it reaches the cells that make vitamin D. At UV 6 with arms and legs bare, 1,000 IU takes roughly 50 minutes for fair skin, 2.5 hours for brown skin and 4 hours for dark brown or black skin.

The scale behind those numbers is the minimal erythemal dose, the UV dose that just reddens skin. In the Fitzpatrick tables our calculator uses, type II sits at 1.5 times the type I dose, type V (brown skin) at 4.7 times and type VI (dark brown or black skin) at 7.8 times (Fitzpatrick 1988; Wacker and Holick 2013). Vitamin D production follows the same ratios, because the melanin that delays the burn is the melanin that removes the UVB.

Melanin is a UVB filter

Vitamin D starts when a UVB photon, 290 to 315 nanometers, strikes 7-dehydrocholesterol in the living layers of the epidermis. In deeply pigmented skin the melanosomes are larger, more numerous and spread through every layer of the epidermis, absorbing UV photons and shedding the energy as heat. Deeply pigmented epidermis passes about 7 percent of UVB to the layers below, against about 30 percent for lightly pigmented skin (Kaidbey 1979). Nothing else changes: the 7-dehydrocholesterol is there in the same amount, and the gut absorbs vitamin D from food identically. Melanin does not make vitamin D and does not block its absorption. It filters the light.

Minutes to 1,000 IU at UV 3, 6 and 9

Estimates from our calculator, not measurements of you: midday in June at 35 degrees north, standing, arms and legs bare (about 42 percent of your skin), no sunscreen, no tan, under 40.

Fair skin, types I and II: 70 to 105 minutes at UV 3; 35 to 50 minutes at UV 6; 20 to 30 minutes at UV 9.
Brown skin, type V: about 5.5 hours at UV 3; about 2.5 hours at UV 6; about 100 minutes at UV 9.
Dark brown or black skin, type VI: about 9 hours at UV 3; about 4 hours at UV 6; about 2.75 hours at UV 9.

At UV 3, where production begins, type VI skin in shorts and a t-shirt gets almost nothing from an hour. Thirty minutes at UV 6 gives type V about 200 IU and type VI about 120 IU, against roughly 600 IU for type II. If you take a photosensitizing medication such as doxycycline or isotretinoin, the burn thresholds behind these figures do not apply to you.

Why deficiency runs higher at high latitudes

Above roughly 37 degrees north, the UV index stays below 3 for two to five months of the year and nobody makes vitamin D outdoors. For types V and VI the season is shorter still: the shoulder months at UV 3 and 4 that top up fair skin contribute almost nothing at a four- to eight-fold dose requirement.

In the United States, 82 percent of Black adults had 25(OH)D below 20 ng/mL, against 42 percent of all adults (Forrest and Stuhldreher 2011). In Manchester at 53.5 degrees north, the summer exposure that brings white adults to 20 ng/mL failed to do so for most adults of South Asian origin (Farrar 2011).

Why most apps get this wrong

The reviews say it directly. "For white skin only. Y'all didn't include any brown people in your research." "Black people are NOT actually black. The options was olive to light brown."

Three failures produce that. The Fitzpatrick scale was published in 1975 with four types to dose phototherapy for white patients; types V and VI were added in 1988, and many apps never adopted them, so the darkest option on screen is a tan. Burn-time apps find that type VI takes hours to redden, report "safe", and say nothing about vitamin D, the number that matters. And vitamin D estimates that do not scale with the minimal erythemal dose hand brown skin a fair-skin number with a small correction.

Sunlight is Life carries all six Fitzpatrick types through its safe-exposure time and vitamin D estimate, and the type can be changed in settings.

Fitzpatrick is an estimate; your skin's response is the measurement

The scale sorts people by appearance and burn history. It does not know your ratio of eumelanin to pheomelanin, and there is no available test for it. Treat the figures above as a starting point and calibrate on your own skin: the dose that leaves faint pinkness the next day is your personal MED. That reddening is an adaptive response, an RNA-stress signal that removes stressed cells and thickens the epidermis (Vind 2024), and a ceiling you do not need to reach.

What to do

Use the midday window, when your shadow is shorter than you. UV 3 is the floor; for types V and VI, the hours at UV 6 and above are what count.
Expose more skin and lie down. Torso, arms and legs is 78 percent of your surface against 42 for arms and legs, and a horizontal body catches a high sun better than a standing one. In a swimsuit, lying down at UV 6, type V reaches 1,000 IU in about 50 minutes and type VI in about 80.
Go often. Several 30 to 60 minute sessions a week at UV 6 or higher beat one long one.
Test 25(OH)D in late autumn and again in spring. The research converges on 40 to 60 ng/mL as the range where bone, immune and metabolic markers look best.

Estimate your vitamin D by skin type, UV index and exposure →

The sunlight quiz places you on the Fitzpatrick scale in two minutes.

Supplements in winter

North of about 37 degrees, plan on supplementing from November to March; for types V and VI, from October to April. If the autumn test is under 30 ng/mL, 2,000 to 4,000 IU of D3 per day is the range most adult trials use, and 4,000 IU is the Institute of Medicine's upper limit. Retest in spring. If you have sarcoidosis, hyperparathyroidism or kidney disease, the dose has to be set against your blood calcium, not this page.

The through line

Dark skin is not a defect in the vitamin D system. It is a UVB filter tuned to the equator, doing exactly what it was built to do, and at 35 or 50 degrees north it needs more sky, more skin, more midday, more often.

Common questions

Does melanin block vitamin D?: In the skin, yes. Eumelanin absorbs UVB photons before they reach the 7-dehydrocholesterol that becomes previtamin D3, so the same UV dose makes less vitamin D in darker skin. Melanin has no effect on vitamin D from food or supplements.
Does dark skin absorb less vitamin D?: No. The gut takes up vitamin D from food and supplements the same way in every skin type. Dark skin makes less vitamin D per minute of sun; it does not absorb less.
Can dark skin get sunburned?: Yes. Type VI skin needs roughly eight times the UV dose of type I to redden, which at UV 9 is a matter of hours rather than minutes, not never. Sunburn is an adaptive inflammatory response that the skin mounts to remove stressed cells and thicken its barrier (Vind 2024), and it runs in every skin type.
Is vitamin D deficiency overdiagnosed in Black people?: It is an open question. Powe 2013 found lower vitamin D binding protein in Black Americans, which would leave the free fraction similar despite a lower total 25(OH)D, and Nielson 2016 traced much of that difference to the assay used. The 25(OH)D test is still the only practical measure, and a level under 20 ng/mL is worth acting on whatever your skin color.
Is the UV index a measurement of sunlight?: No. The UV index is a sunburn-weighted score: solar UV weighted by how efficiently each wavelength reddens skin, then summed. UVB dominates that weighting and UVA barely registers, so the index is a proxy for burn risk and says little about the rest of the light. Two moments with the same index can carry very different spectra.
How does Sunlight is Life calculate UV?: It runs a solar physics engine that models the actual sunlight reaching your coordinates, not the nearest city, and shows the UVA and UVB you are receiving separately, updating while the app is open. Your Fitzpatrick type does not change that number; it changes the safe-exposure time and vitamin D estimate built on it. It is still a model, not a measurement of your sky.