Vitamin D

Vitamin D is used in the body for many different things. It is important for good immune system function and to prevent infections.

Even in the summer, it is hard to get enough sunshine to let the body produce it due to our typical wage slave lifestyle. A lot of time is spent indoors during the day. Outdoor workers wear protective clothes to avoid sun burns and skin cancer and may also not get enough.

The older we get, the harder it is for our bodies to produce vitamin D from sunshine.

Get tested. Then supplement to get into the optimal range.

60-80 ng/ml is the optimal range.

4000 IU per day should be the maintenance dosage after optimal blood levels have been reached.

If possible, split up the dosage into multiple smaller ones (e.g. 2000 IU in the morning, 2000 IU in the evening).

Starting point for your own further research: Vitamin D Wiki

Natural sunlight is important not just for vitamin D production. You will need to weigh the risk of getting skin cancer from sunburn and too much sunshine with the risk of not getting enough.

It is probably a good strategy to exposure yourself for a short time (e.g. 5 minutes) to natural sunlight around noon every day. For longer daytime activities in the sun, protect yourself with a zinc-based sun screen and wide-brimmed hat.