After a long winter trapped inside the house, anyone can appreciate the wonderful feeling of a day in the sun. The effect is not simply due to the fresh air and warm breeze. Vitamin D, synthesized in the skin from sun exposure, has been shown to decrease anxiety and depression, and reduce the risk of developing heart disease and certain types of cancer. However, too much time in the sun can increase the risk of developing skin cancer. For those of you wondering how to strike the right balance, I’ll recap the current science on sunlight, vitamin D and health.
Vitamin D deficiency is increasing around the globe. For most of human existence, time in the sun was essential for survival. In our modern world, most people spend little time in the sun, and when they do, they are often covered in clothing and sunscreen, thereby limiting their body’s ability to produce vitamin D.
Traditionally, vitamin D deficiency was mainly a concern for bone health. Now, while the data is somewhat inconsistent, there is general agreement in the scientific community that low vitamin D levels increase the risk of developing colorectal, prostate, breast, and other types of cancers. In addition, vitamin D metabolites may protect against cardiovascular disease, autoimmune disease, and infections. Furthermore, a meta-analysis found a 29% reduced risk of death from all causes in individuals with the highest levels of vitamin D compared to those with the lowest levels. An efficient way to increase vitamin D levels in your body is through sun exposure, but sun exposure increases the risk of skin cancer.
There are two classes of skin cancer, melanoma and nonmelanoma skin cancers (including basal and squamous cell carcinomas). Melanomas often spread if they are not caught early. While melanomas only account for 3% of skin cancers in the U.S., they result in 75% of skin cancer deaths. Nonmelanoma skin cancers generally do not spread to other parts of the body, though they can result in disfiguration.
Sunburns, especially for children, are of concern when it comes to developing skin cancer. Intense sunburns early in life are closely associated with the later development of melanoma. Having more than one severe sunburn in childhood is associated with a 2-fold increase in melanoma risk. The relative risk of developing skin cancer is three times higher in children born in areas with high levels of UV radiation versus people who move to those areas as adults.
While the negative consequences of excessive sun exposure seem to be the greatest in childhood, they do not end there. While intermittent intense sun exposures increase the risk of developing melanoma and basal cell carcinoma, chronic UV exposure is associated with increased risk of squamous cell carcinoma. Furthermore, the risk of developing nonmelanoma skin cancers is 2-3 times greater in people using tanning beds.
How can you maximize the positive effects of vitamin D while minimizing risk of developing skin cancer? One alternative to sun exposure is to take vitamin D supplements. There are two types of vitamin D, D2 and D3. Vitamin D2 is synthesized in plants. Vitamin D3 is synthesized in animals. Two studies (1, 2) found that vitamin D3 is more efficiently absorbed by the body than D2. However, a newer study found vitamin D2 to be absorbed as efficiently as D3. If eating animal products is not a concern, opting for vitamin D3 is probably the best option.
What is the optimal level of vitamin D? The Institute of Medicine recommends a serum 25-hydroxyvitamin D (the form of vitamin D in the blood stream) level of 50 nmol/l to prevent bone deterioration. However, the science seems to indicate levels of 75-87.5 nmol/l, or even up to 110 nmol/l, is optimal to reduce risk of cancer and heart disease. The later study suggests consuming 1,800-4,000 IU of vitamin D per day to achieve these levels. If you’re curious about your vitamin D level, consult your doctor for a blood test.
It seems that healthy vitamin D levels can be reached through dietary supplementation. Nonetheless, taking a dose of vitamin D has never given me the same great feeling of a day outside in the sun. There may be more benefits of sun exposure, besides vitamin D production, that science is yet to discover. I’d advise people to enjoy the sun, but to use sunscreen during prolonged periods outside to avoid burns, and be especially cautious of sunburns for children.