Why daylight matters. UVB light can help uncovered skin make vitamin D, although the amount varies with season, latitude, cloud cover, skin pigmentation, age, clothing, and sunscreen. Bright daytime light is also one of the strongest cues for the body’s circadian clock. Protect your skin, avoid burning, and treat this planner as travel inspiration—not a vitamin D prescription or medical treatment.
NIH vitamin D facts · NIH circadian rhythms