Summer is my favorite time of the year simply because it is warm and the sunlight makes me feel good. In the winter, the sunlight frequents us much less often- but does that affect us?
On average, humans used to spend at least half a day exposed to sunlight before electricity. Nowadays, exposure to sunlight is highly discouraged for fear of skin cancer and modern lifestyles are built around spending long hours inside exposed to artificial light. There is evidence that Ultraviolet Radiation (UVR) in the form of sunlight is a significant factor for non-melanoma and melanoma skin cancers in pale skinned people. Since our skin is a very large organ, about two square meters in an average adult male, exposure to the sun- whether risky or beneficial will impact us significantly. Similar to stroke, rates of acute coronary syndromes (including unstable angina, acute myocardial infarction, atrial fibrillation and sudden cardiac death) are highest in the winter months with shorter hours of sunlight.
Two benefits of sunlight:
Vitamin D: Vitamin D is formed when ultraviolet B (UVB) hits the skin and mediates photolysis of 7-dehydrocholesterol in the skin.
Melatonin: Melatonin is produced from serotonin by the pineal gland located in the center of the brain during periods of darkness, and its release is suppressed as a function of visible light intensity sensed through ocular photoreceptors.
In the 1970’s it was observed in several studies that people had consistently lower blood pressure in the summer than in the winter. It was found that the prevalence of mean population diastolic and systolic blood pressures correlate directly with latitude, being higher in populations living further from the equator. Recent studies have also confirmed this by demonstrating that biologically relevant doses of UVA lead to a sustained reduction in blood pressure. With a reduction in blood pressure, and a 20 mmHg lower systolic blood pressure- this leads to a two-fold reduction in overall mortality in both men and women aged 40-69 years. With this in mind, moderate exposure to sunlight may also reduce the economic burden of CVD. One study estimated this amount to be $519 Billion for hypertension, heart disease, and stroke in the USA (Combined impact of healthcare costs and lost economic output).This could potentially translate into hundreds of thousands of person- years of life and $Billions saved each year- (What a convenient way to boost our economy!).
If you have read my past articles, you know that I am a fan of arginine and Nitric Oxide (NO). In a recent study, it was found that moderate exposure to sunlight may activate bound stores of NO in the skin and mobilize it to its bioactive form. Nitrites, a byproduct of NO has long been considered biologically inert at low concentrations, but is now known to not only dilate blood vessels on its own, but to protect organs against ischemia/ reperfusion. Skin bound NO stores are in equilibrium with circulating nitrite in un-irradiated individuals, and dietary-derived nitrite may therefore increase the skin “NO” reservoir. Nitrite and NO are generated on the skin surface by reduction of sweat nitrate and possibly the oxidation of ammonia. A recent study demonstrated that UVA irradiation can increase plasma nitrite levels by 40%. The adult cardiovascular system may be more susceptible to the beneficial effects of sunlight- related NO release compared to children considering that the demographic is transitioning to an ageing world population with enhanced CVD.
So……… Next time the sun hits your face and you feel its warmth- remember—It might be doing much more for you than you think!
Is sunlight good for our heart? (2010). European Heart Journal, 1-5.