-Dr Prashant Makhija, Consultant Neurologist, Wockhardt Hospital, Mumbai Central
The mighty Sun though itself has an inhospitable environment but its light is necessary for the sustenance of life on our planet. Sunlight is essential not only for our physical health but also influences our psychological health. The mechanism by which it affects our mood and psychological health is related to regulation of melatonin and serotonin secretion.
Pathway- Sunlight & Mood
Our circadian rhythm is regulated through ‘suprachiasmatic nucleus’, having connections with the retina as well as the ‘pineal gland’ which secretes melatonin. Exposure to daylight suppresses melatonin production whereas levels of its precursor, serotonin is also known as ‘happiness hormone’ are elevated.
Serotonin and Its Impact on Mood and Seasonal Variation in Depressive Disorders
Upregulation of serotonin creates a sense of well-being, contentment and elevates our mood. This also explains the seasonal variation seen with depressive disorders, which are more likely to be observed in late fall and winters. It is for this reason; phototherapy is advocated as one of the treatments for depression. Studies have suggested our cognitive functions may also be potentially affected by sunlight exposure through the involvement of similar pathways.
Sunlight is necessary for the production of vitamin D, accounting for over 90% of the requirement for most individuals. Adequate Vitamin D levels are a must for bone health. Deficiency of Vitamin D has also been associated with autoimmune disorders such as Multiple Sclerosis, Lupus, and Rheumatoid arthritis.
It has been reported that people with inadequate exposure to sunlight and deficient Vitamin D levels such as those living at higher latitudes are at increased risk of dying from Hodgkin lymphoma, as well as breast, ovarian, colon, pancreatic, prostate, and other cancers, as compared to those living at lower latitudes. Some studies have also demonstrated an association between low Vitamin D levels and poor cardiovascular health and increased risk of Diabetes.
In spite of the innumerable benefits of sunlight exposure, it is important to point out that excessive exposure increases the risk of skin cancer; more commonly observed in residents of Australia and New Zealand.
As multiple factors influence sunlight absorption, such as time of day, season, altitude, and skin pigmentation, it is difficult to make universal recommendations regarding sun exposure. While some suggest exposure to the arms and legs for five to ten minutes, two or three times per week, maybe beneficial for maintaining vitamin D sufficiency (though inadequate for treatment) while others recommend exposure for 3–15 minutes for whites and 15–30 minutes for blacks when the sun is highest in the sky, with 40% of the skin problem