Does sunbathing increase 25-hydroxyvitamin D?

Generally speaking, sun exposure can increase the level of 25-hydroxyvitamin D. The detailed explanation is as follows:

When human skin is exposed to ultraviolet radiation, 7-dehydrocholesterol in the skin converts into vitamin D3. Vitamin D3 is then hydroxylated in the liver to form 25-hydroxyvitamin D. This is the primary storage form of vitamin D in the body and also an important indicator reflecting the body's vitamin D stores. It is recommended to wear short sleeves and shorts when sunbathing, allowing more skin to directly contact sunlight, which helps improve the efficiency of vitamin D synthesis.

Different skin types, age, and other factors can affect the efficiency of sun exposure. People with darker skin tones require longer sun exposure to synthesize the same amount of vitamin D due to higher melanin content in their skin. In addition, elderly individuals and those who are obese may also require more sun exposure to maintain normal vitamin D levels.

It is recommended to moderately expose the skin to sunlight during periods of strong sunlight, while avoiding prolonged exposure to prevent sunburn.