After 15 minutes of sun exposure, which of the following people would have synthesized more vitamin D?

Question

BlackTom AI · Accepted Answer

Context: The question compares vitamin D synthesis after 15 minutes of sun exposure for different skin tones.
Option 1: "A light-skinned person". Light skin has lower melanin content, which means less natural UV filtration. As a result, UVB photons reach the epidermal cells more readily, driving the photochemical conversion of 7-dehydrocholesterol to previtamin D3 more efficiently. Therefore, after a fixed, short exposure like 15 minutes, a light-skinned person would typically synthesize more vitamin D.
Option 2: "A dark-skinned person". Darker skin contains more melanin, which absorbs more UVB photons. Although this protects against UV damage, it also slows the rate of vitamin D production. Consequently, for the same 15-minute exposure, a dark-skinned person would generally produce less vitamin D than a light-skinned person.
Option 3: "They would both synthesize the same amount". This would imply equal UVB effectiveness regardless of melanin, ignoring the key role melanin plays in filtering UVB. In reality, melanin concentration creates a significant difference in synthesis rate, so this option misstates the biology.
Overall, the reasoning hinges on the relationship between skin melanin content and UVB penetration: higher melanin reduces UVB penetration and delays vitamin D synthesis, whereas lower melanin allows more UVB to reach the vitamin D precursor and increase production for the same exposure duration.
In summary, the comparison hinges on skin pigmentation: lighter skin allows more rapid vitamin D synthesis with the same sun exposure than darker skin, while the notion of identical synthesis in both is inaccurate due to melanin's UV-filtering effect.

HUMNNTR 2200 SP2025 (15810) Learning Module: Bone Health

After 15 minutes of sun exposure, which of the following people would have synthesized more vitamin D?

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