I know it may seem a bit early to start talking about ultraviolet (UV) exposure, sunscreen and skin cancer, but I plan to be back on my bike as soon as the snow melts to get a head start on spring. I think that a discussion about skin health is appropriate for this blog.
Let’s be honest, marathoners and triathletes and others who spend a lot of time outdoors sometimes look older than they really are. Sun damage results in premature aging, also known as photoaging, and it can promote the development of skin cancer. We all know that too much exposure to sunlight has adverse effects, but I am going to explain some of the science behind it.
Exposure to the sun affects cells in multiple ways. One negative aspect of exposure to UV light is that it causes changes to the structure of DNA, which can result in the formation of a mutation. DNA is comprised of only four basic building blocks: adenine, guanine, cytosine and thymine. These bases can be chemically modified during our lifetimes, which can cause alterations in the protein sequences that are encoded by genes. Some changes to protein sequences are detrimental and can promote diseases such as cancer. One way UV modifies DNA is by inappropriately linking thymines together with one another into what is known as a thymine-thymine dimer. This causes a kink in the DNA double helix that needs to be repaired via a DNA repair mechanism. I rarely discuss the mechanisms of DNA repair in my classes because although they are very important, the details are boring. That is just my opinion though. If the kink is not repaired properly, the wrong DNA building blocks can be put in the wrong place, potentially causing a mutation. The direct modification of DNA by UV light can eventually lead to enough mutations that cause skin cancer.
Because thankfully few of us sit around and worry about getting cancer later in life, please allow me to scare you into wearing your sunscreen using a different argument. Too much sun will make you look old. We all know this but how does it work? Cells are connected to one another through a structure called the extracellular matrix. This matrix is comprised of large proteins that provide a means for cells to remain attached to where they should be and to provide structural integrity to our tissues. The matrix can be broken down by secretion of proteins called matrix metalloproteases, proteins that break down other proteins. UV exposure can promote an upregulation of matrix metalloproteases, causing a loss of collagen and other proteins in the extracellular matrix. This ultimately results in the formation of lines and wrinkles.
Although being able to exercise outside is enjoyable and overall healthy, I try to limit my sun exposure by wearing sunscreen. Being a long distance runner or serious cyclist will promote good cardiac health and the maintenance of a healthy weight, but consistently exposing yourself to the sun results in the accumulation of harmful changes to your skin. We probably all want a beach body, but no one is going to look if your skin does not look good. Being a healthy weight only gets you so far.
As for how much sun exposure is healthy, who knows. I personally do not think anyone anytime soon will have an answer to that question. It is important to note that the sun also has health benefits, potentially in the context of allergies and asthma. Because allergies and asthma are on the rise, scientists and clinicians have been spending a lot of time trying to figure out why this is the case.
UV light stimulates the production of vitamin D, an important molecule in both bone health and immunity. It has been hypothesized that reduced vitamin D levels promote the development of asthma and allergies. Many more studies are needed to support this argument, including studies that examine the appropriate dose that we need. It has been reported that both low and high amounts of vitamin D are correlated with the development of immune problems, but scientists and physicians do not have a consensus of what is “low” and what is “high”. When thinking about correlations alone, the argument that a lack of sun exposure is playing a role in the development of allergies and asthma makes sense. It has been documented that people, particularly in Western countries, are getting less and less sun, even if you live in a warm, wonderful climate. Thus, it is conceivable that a reduction in vitamin D could be promoting unwanted changes to human health. Let’s be honest again, few people walk or bike anywhere or spend much time outdoors. Most Americans go from their garages, straight to the parking lot at work (which is usually right next to the door), and back home again without seeing the sun for more than a few minutes a day. I used to live in a part of the country where everyone drives everywhere.
What is the solution to the problem that the sun will make us look old but also likely keeps our immune systems healthy? I don’t have an answer to that, but what our society is doing now is not working. Our sedentary lifestyles are likely to blame for an array of diseases. I personally like to walk or bike whenever I can, and thus I spend a lot of time outdoors. I wear an SPF and don’t worry if I miss a spot since maybe I’ll be getting an optimal dose of UV for the day (that is just a guess since this issue hasn’t been fully resolved). So, my advice is to continue exercising outside, but remember that wrinkles are unattractive and thus don’t leave without the sunscreen. Most things are okay if you have the right dose, whatever that is.
Litonjua, AA. (2012) Curr Opin Allergy Clin Immunol. 12:179-185.
Pandel, R., Poljsak, B., Godic, A. & R. Dahmane. (2013) ISRN Dermatology