Perhaps I should have elaborated more on the vitamin D and cancer connection. I doubt anyone will actually watch that one-hour vitamin D lecture I posted a link to, and I know everyone's been told for years to stay out of the sun because it'll give you skin cancer. So simply telling you that sun exposure reduces cancer rates probably isn't convincing. Allow me to explain myself.
First off, how serious is the skin cancer problem?. One look at the cancer statistics from 2010 shows that non-melanoma skin cancer is surprisingly benign. In 2010, less than 1,000 people in the United States died from skin cancer. That's about 0.0003% of the population, and less than 0.2% of total cancer deaths, according to the National Cancer Institute's statistics. There are at least 12 other types of cancer that are more deadly. Perhaps the problem has been a bit overstated.
But on to the task at hand. Let me begin with these two maps... the one on the left shows the amount of UVB radiation received across the nation, and on the right is a map of breast cancer prevalence. There are maps like this for all types of cancer, and they all show similar patterns.
They're strikingly similar. Areas with more UVB exposure, the type of sunlight that your skin uses to make vitamin D, tend to have lower cancer rates. Here's another chart, this one's pretty old, but still very relevant...
Cities that see more solar radiation from the sun have lower rates of breast cancer. But like I explained in my last post, correlations like these don't indicate causality. That's where the new research on vitamin D comes into play. High blood levels of vitamin D, 25(OH)D, are clearly associated with a lower risk of cancer. According to this study, supplemental vitamin D combined with sun exposure is enough to raise blood levels of vitamin D to 52 ng/ml, a level that is associated with a 50% reduction in the incidence of breast cancer. Another study, this time a controlled, clinical trial, tested the impact of vitamin D and calcium supplementation on cancer rates in postmenopausal women. The study showed that the group receiving both vitamin D and calcium, as opposed to just calcium, or a placebo, showed a "60% or greater reduction in all forms of cancer." Very significant.
Let's put this all together. Climates receiving more UVB exposure from the sun, the type that forms vitamin D in our bodies, are associated with lower cancer rates. High vitamin D blood levels are associated with lower cancer rates. Vitamin D supplementation significantly lowers the risk of developing cancer. Add to this the fact that it makes evolutionary sense that the sun would be beneficial for us: When humans migrated further and further from the equator, their skin became lighter and lighter, becoming more efficient at making vitamin D through limited sun exposure. And while we're at it, throw in some common sense too: Why would the very thing that gives us life on earth, the sun, kill us at the same time? Connect the dots, and it looks like sun exposure probably prevents cancer more than promotes it. At least that's my interpretation of the evidence.
Now I'm not saying you should go out in the sun and tan all day long to the point where you burn. That's not good for anybody. However, it is completely unnatural to avoid the sun altogether. There's nothing wrong with moderate sun exposure. And take it easy on the sunscreen. Sunscreen prevents UVB absorption, meaning you won't get burned but you also won't make vitamin D. If you'll be in the sun all day, at least hold off on the sunscreen until you've had a chance to get the benefits of sun exposure.
Could it be that the conventional medical advice to stay out of the sun has actually caused more cancer than it has prevented?? Let that marinate for a while.