There seem to be quite a few 'on-the-rise' campaigns for re-raising awareness of the importance of vitamin D.
Vitamin D is the 'vitamin' that is gained mainly through sunlight exposure. Actually, vitamin D is not strictly a vitamin, but a steroid hormone.
Dr. Mercola is the author of Dark Deception--Discover the Truth about the Benefits of Sunlight Exposure. He is a strong advocate of going out and getting adequate sun exposure in order to boost vitamin D intake.
Here are notes from his video:
Vitamin D influences 2,000 genes, hence it's essential for so many diseases. Dr. Mercola cites autoimmune diseases and cancers as key diseases linked to vitamin D deficiency. Vitamin D is also good in aiding people with high blood pressure. There are also some studies that suggest rise of autism being linked to increased vitamin D deficiencies. Vitamin D is also an antibiotic, as well as being beneficial for eczema, insomnia, matricular degeneration, periodontal disease, and hearing loss.
Vitamin D aids calcium uptake (although remember from previous Margo Peinemann lecture, zinc is also an important partner in calcium absorption).
It has long been held that people who live further away from the equator are more likely to have vitamin D deficiency. Dr. Mercola shows a map of the US which shows a correlation between certain diseases - namely cancers - and the fact that they are more concentrated further north.
Ultraviolet light/radiation is broken down into UVA and UVB. It is UVB that contributes to the formation of vitamin D in the body. You need four UVB photons combined with one molecule of cholesterol (7-DHC), opening a ring to make vitamin D3. The liver converts vitamin D3 to 25(OH)D ("25 hydroxy D").
It is recommended to be regularly tested for vitamin D levels, since it's important to tailor a vitamin D intake program that's just right for your particular case. The dangers of overdosing on vitamin D supplements is not known as yet. Levels of less than 50ng/ml indicate vitamin D deficiency. Another indicator of vitamin D levels can show up in calcium serum levels. If calcium levels are really high, it suggests that vitamin D levels are probably too high.
In relation to the risk of sun-related skin cancer, it is true that there is an increase in skin cancers while the overall time we spend outdoors is less. Possible speculation on why this could be is that it could be down to an increase in omega-6 levels from high-fat diets. Or it could be the way that we don't gradually build up exposure to strong sunlight. Or it could be a result of applying toxic chemicals in the sunscreen to our skin. In addition, with sunscreens, they generally block out UVB radiation (beneficial to vitamin D production) more so than UVA radiation (this is the UV radiation that tends to cause the cancer).
Ageing can reduce the ability to synthesize vitamin D. Dark skin pigments also hinders vitamin D absorption. Covering the skin also prevents vitamin D absorption. Glass also blocks out UVB, so it is not particularly beneficial to sit at a window in the hope to gain vitamin D. In the winter time, it is very difficult to get adequate vitamin D exposure. As a tip, the shorter your shadow in the sun, the more vitamin D exposure you are likely to be getting.
Dr. Mercola does support the use of tanning beds, but adds that they must be safe tanning beds. He starts to go on to say what he means by safe, and it looks like he has other videos on his YouTube channel about tanning beds.
He doesn't particularly advocate vitamin D2 which is added to some foods as 'supplements'. D2 shuts down vitamin D3 conversion, so he doesn't believe it is a good idea to ingest it. However, there are few ways to get vitamin D into the body through food forms. He does promote supplements if absolutely needed, although they should be taken with regular monitoring through blood tests. He comments that the half-life of vitamin D from the sun is about 4-6 weeks, whereas in contrast, the half-life of vitamin D from oral supplements is about 4-6 months, which gives some indication of how different the different types of vitamin D intake can be.
Dr. Mercola also advises against using soap in a shower that follows being out in the sun for at least an hour after exposure, since the skin needs time to absorb the vitamin D from the sun.