While too much exposure to the sun can be dangerous, there are consequences to avoiding the sun altogether.
It’s Spring: the time of year when I’m asked almost every day about sun exposure, sunscreens, and other related questions. There are some points about which we all agree: sun exposure leading to burned skin is dangerous, for example. However, there remains disagreement among healthcare professionals about the safety of spending time in the sun and the consequences of avoiding it.
Humans produce vitamin D in response to sun exposure. It is not found in foods, and therefore, we can conclude that humans need sunlight. The sun has contributed to our survival; there were no fortified foods and vitamin D pills until recently, which means that we relied on sunshine to stimulate production of vitamin D, which is actually a hormone that was misclassified as a vitamin.
Researchers reported in a March 2016 article that women who avoid the sun have a shorter life expectancy than women who do not, and that the effect was dose dependent. More sun exposure resulted in lower risk of cardiovascular disease and non-cancer/non-CVD deaths, while lower sun exposure resulted in higher risk. In fact, the researchers say, avoiding sun exposure resulted in the same risk for all-cause death as smoking. Sunshine even offered some protection to smokers: 60-year old smokers who spent the most time in the sun had a life expectancy two years longer than smokers who avoided it. This indicates that avoiding the sun “is a risk factor for death of a similar magnitude as smoking,” the authors wrote.
The study included 29,518 Swedish women who were followed for 20 years. One of the differences between this and other similar studies was the analysis of a dose-dependent relationship of sun exposure; other studies have compared people at the upper extreme of sun exposure with those who completely avoid it. The researchers acknowledge limitations which include that the study was observational and did not involve investigation of a cause-and-effect relationship. One of the confounding factors is that sun exposure is often accompanied by other healthy lifestyle habits.
The researchers offered several explanations as to why there is a relationship between higher sun exposure and lower risk of mortality. They referenced studies showing that there is an inverse relationship between vitamin D levels and type 2 diabetes, and differences in hemoglobin A1c levels depending on the season. Studies show that those living closer to the equator have a lower risk of type 1 diabetes.
Cardiovascular disease is also related to sun and season. People who spend more time in the sun have a lower incidence of thromboembolism, and also a lower risk of developing high blood pressure. Winter is associated with an increased risk of heart disease, stroke, and arterial and venous thromboembolism.
An evaluation of the effects of sun exposure on patients with skin cancer showed that the risk of all-cause mortality increased four-fold in subjects who had non-melanoma skin cancer (NMSC) and multiple myeloma as a result of avoiding sun exposure when compared to the group that had the highest amount of sun exposure. They cited studies reporting increased survival rates for skin cancer patients who spent time in the sun. The group concluded that sun exposure may increase the risk of skin cancer but does not decrease life expectancy. “We did find an increased risk of… skin cancer. However, the skin cancers that occurred in those exposing themselves to the sun had better prognosis,” researcher Dr. Pelle Lindqvist said.
The group offered several suggestions as to how to interpret the results of the study. First, advice about sun exposure and restriction should vary by geographic area. In northern latitudes where the UV index is low, less restriction may be better, for example.
They note that research shows that using sunscreen does not make it safer to be exposed to the sun for longer periods of time, and challenge the advice that essentially gives people permission to stay in the sun for as long as they like as long as long as they use sunscreen. They note that the rising skin cancer rate in Sweden has been a result of over-exposure to sunlight since the Swedes have developed a dependence on sunscreen and that advising restriction of sun exposure through the use of sunscreen may be responsible for the increased incidence of CVD and non-cancer/non-CVD morbidity and death in Sweden. Dr. Lindqvist said this about sunscreen: “If you’re using it to be out longer in the sun, you’re using it in the wrong manner,” he said. However, “If you are stuck on a boat and have to be out, it’s probably better to have sunscreen than not to have it.”
This and other similar studies have led many professionals to conclude that the main value of sun exposure is vitamin D and to therefore, recommend vitamin D supplements. But the group cautioned against interpreting their study to mean that differences in outcomes based on sun exposure were related to vitamin D. They say that Vitamin D may just be a marker for sun exposure and that the benefits of sun have more to do with other mechanisms related to UV radiation.
The idea that vitamin D pills can promote better health is still promoted by many health providers, but growing body of evidence does not support the theory. Observational studies show that people with many health conditions have lower vitamin D levels, but intervention studies – giving vitamin D supplements to people with these various conditions – have not shown that the pills improve health. Researchers involved in these studies say that lower vitamin D levels are a result of disease, not the cause of it. In view of this recent research, it may be that there is an effect of sunshine that includes but is not limited to vitamin D production.
Dr. Lindqvist told Medscape “We know in our population, there are three big lifestyle factors [that endanger health]: smoking, being overweight, and inactivity. Now we know there is a fourth — avoiding sun exposure.”
- Lindqvist P, Epstein E, Nielsen K, Landin-Olsson M, Ingvar C, Olsson H. “Avoidance of sun exposure as a risk factor for major causes of death: a competing risk analysis of the Melanoma in Southern Sweden cohort.”Journal of Internal Medicine, Published online March 16, 2016
- DOI: 10.1111/joim.12496
- Autier P, Boniol M, Pizot C, Mullie P. “Vitamin D status and ill health: a systematic review.” Lancet Diabetes and Endocrinology Jan 2014;2(1):76-89
- Marcia Frellick “Avoiding Sun as Dangerous as Smoking.”
- Medscape March 23, 2016