Should we seek the shade all day or just during the midday sun. Here is what I have come to believe. For thousands of years humans spent lots of time in sunshine, some with minimal clothing. Our skin pigmentation evolved as we migrated out of Africa, getting more transparent, perhaps, to ensure that we receive more of the benefit from the weaker suns rays in the higher latitudes. Maybe this is because it is very important for our health.
A few decades ago we regularly treated some ailments with sun exposure. TB treatment is the most obvious example. It is fascinating that some diseases such as MS correlate with latitude. The further you are from the equator, the higher the risk of Celiac disease, Type 1 diabetes, rheumatoid arthritis, Crohn's disease, lupus, psoriasis and MS. This is from the American MS website: https://mymsaa.org/ms-information/overview/who-gets-ms/
Individuals living beyond the 40-degree mark north or south of the equator are far more likely to develop MS, and this is especially true for people in North America, Europe, and southern Australia
UV rays in sunshine are categorized into UVA with a longer wavelength and UVB with a shorter wavelength and they are different in the impact they have on the human body.
UVA with its long wavelength is able to penetrate glass, the atmosphere and penetrate deeper into skin. As a result of this it is more responsible for creating a tan as the skin responds to this insult and increases the level of melanin for natural protection. By gradual exposure to this effect , it seems that we may be able to build up a protective layer that will minimize skin damage and possibly protect against skin cancers. I understand that skin cancer risk is very high in office workers and maybe this is due to a lack of regular sun conditioning.
I read that we should not equate skin damage to getting a tan. A tan is not skin damage. Skin damage comes for the intense action of UVB. However skin damage will most certainly occur whilst getting a tan if the concurrent UVB exposure is high or prolonged.
UVB has a shorter wavelength and is much more dangerous, creating sunburns which can apparently confer life long cancer risk. Because of its short wavelength, UVB is filtered by the atmosphere and so should be avoided during the middle of the day when it is directly overhead and has less atmosphere to be filtered through. It is suggested that if you are sunbathing for health, then do so when your shadow is longer than your height, because this will be the time that the atmosphere is filtering out most of the harmful UVB rays. Sunburn will cause DNA damage so should be definitely avoided.
With sun exposure your body makes vitamin D from cholesterol. Many studies have shown that this exposure correlates with higher levels of natural immunity, improves sleep and reduces the risk of many diseases. Surprisingly the same impact of vitamin D has not been able to be duplicated with supplementation, which is perhaps related to this next point. Sun exposure also helps your body create nitric oxide which is very important for your health. It is critical for blood pressure control and for the blood pumping action of arteries and veins. The little blue pill defeats ED by the action of the nitric oxide it helps create.
A Scandinavian study set out to look at the impact of sun exposure on longevity. They found that on average higher sun exposure people benefited from longer life. See:-
https://pubmed.ncbi.nlm.nih.gov/26992108/ below is part of their conclusion
Nonsmokers who avoided sun exposure had a life expectancy similar to smokers in the highest sun exposure group, indicating that avoidance of sun exposure is a risk factor for death of a similar magnitude as smoking. Compared to the highest sun exposure group, life expectancy of avoiders of sun exposure was reduced by 0.6-2.1 years.
It is puzzling to see the massive growth of skin cancers over the last few decades given the high levels of sun exposure of our ancestors. Is it due to a much greater focus on finding this damage, to lower ozone protection, or is something else at play here. If the increasing levels of skin cancer are compared with the level of polyunsaturated seed oils (PUFA’s) in the diet, there is a very close correlation. Maybe this is significant. PUFA’s will replace saturated fat in cellular membranes and the level of these fats is growing rapidly in the skin of humans on the standard American diets of today.
A healthy person has about 2% PUFA in their body fat, however many people these days have up to 30% PUFA in their body fat. These polyunsaturated seed oils, have only been part of our diet since 1911, and come as soy bean oil, corn oil, safflower oils, rice bran oil, sunflower oil, etc. They are very prone to oxidation due to the molecular structure and it is believed by some that they can promote oxidation in the whole body. Cellular membranes are critical to health as they are part of every cell and if compromised by oxidized oils may be accelerating problems such as whole body inflammation, fatigue, and the risk of cancers. Conversely saturated fats which up until the late 1900’s were the most common dietary fats, are very resistant to oxidation due to their hydrogen-saturated molecular structure and lack of double bonds.
Some people who have adopted diets that shun PUFA seed oils, replacing them with saturated fats, are claiming that they suffer from less sunburn, can spend more time outdoors without discomfort and keep their tans for much longer. Because seed oils have a half life in the human body of about 2 years, and are endemic in ultra processed food, restaurant fryers and fast food, it will take a long time for someone to know if this impact is also their experience. This needs to be researched further as it could be much healthier than slathering your skin with dubious (possibly carcinogenic) chemicals in order to reduce UVB sun damage.
Some chemicals and food can make skin more sensitive to sun damage. Lack of vitamin B3 (Niacin or Nicotinamide) and lack of vitamin B12 (Cobalamin) make people more sensitive to sun damage, in fact some believe that B3 can reduce the risk of skin cancer by actively assisting with sun damage repair. Artificial sweeteners, some citrus fruits, figs, parsley, celery, dill, fennel and NSAIDS are reported to increase photosensitivity in human skin for some people.
Find my book at https://amzn.to/3uiehfv Seek professional medical advice before making dietary changes, particularly if you have underlying health problems.
Good health, George Elder, Diet Researcher, Dip. Nutrition.