To set your circadian rhythm, consider factors like the weather, your skin tone, and how close you live to the equator. However, this doesn’t mean you should skip sunscreen—it’s still essential for protecting against free radicals and preventing skin cancer.

The best way to check your vitamin D levels is through a blood test. This removes the guesswork, helps you understand your baseline, and guides the right steps to take. (Optimal levels are above 30 ng/ml.)