Sun gives warmth. Sun gives light. Sun gives colour to the sky. The change in the colour of sky when the sun is rising or when it is setting is vivid and it is different on different days and different at all moments. The feeling is exhilarating, seeing the sun rise on the hills, specially in Nagarkot in Nepal when actually you see the sun rise from below to the top above the seven hills one on which is Everest. The sun dipping in the sea has its own charm. When the sun sets it acquires a colour apart from its life-giving qualities.
The sun can be blazing and hot in summer in the deserts of Rajasthan. The air is hot as if it is blowing straight from the oven. It can burn the skin and give sun-stroke. It is the energy source of all life. Above all it is most important for our overall immunity and physical and emotional stability.
The Sun God is worshipped by Hindus. They offer water and prayers to the sun every morning after bath. The Sun is important for the very existence of life on earth: the plant life, marine life and animal life. The effect of the rays of the sun directly spreading on the human body, with which we are here concerned, may be of some nuisance to us in the tropics.
The effect of sunlight is two-fold as it causes:
Photochemical reactions;
Heating effect
Sunlight is important for a proper growth, specially of our young ones. We know now that the solar ultraviolet radiation is necessary for synthesis of calciferol, the forerunner of vitamin D. Calciferol is released into the blood stream by the skin. This hormone is released when sunlight falls on the skin. Without calciferol not enough calcium would be laid in growing bones. Where it is not available, one comes across crippling deformities and rickets. Adequate sunlight is necessary for a proper growth of bones and the prevention of rickets.
The photochemical effects are restricted to limited spectrum region. The vision for example falls between approximately 0.4 m and 0.65m wave lengths of sun light rays which is important part of sun light. When sun light reaches the surface of the earth it passes through atmosphere. The ozone layer of atmosphere absorbs the ultraviolet and infra red rays are absorbed by water vapour, smoke, dust, gas molecules, water drops, etc. This foreign matter effects the quality of sun light.
Solar radiation may be blocked by many means. Among them is industrial smog seen in Mumbai and London and other polluted places. The long dark winter of North India and many North European countries, also leads to a forced and prolonged confinement of infants indoors during the winter. This affects their health.
In 1908, Theobald Palm, an English Medical Missionary who went to Japan was surprised to find the absence of rickets among the Japanese exposed to sunlight. Harry S. Hutchinson who conducted an investigation in Mumbai in the beginning of the century, found no rickets among poor Hindus who ate poor and inadequate diet but who worked outdoors all the day and while at work left their infants at some nearby site in the open air.
In contrast, he found that rickets was common among wellfed members of other castes and upper class Hindus, whose women normally married at the age of 12 and whose offsprings usually remained with their mothers for the first 6 months of life in semidark rooms in the interior of the house.
Hutchinson concluded due to lack of sunlight, fresh air and exercise that children suffered. He proved the point by removing 10 children from enclosed “purdah” environments and keeping them out in the open air. They were all cured. Rickets cause swelling at the end of the long bones. Growth is retarded by the failure to make new bone. Due to defective mineralization, the bones become soft and weak and develop curvatures.
The human skin can generate an adequate amount of vitamin D if exposed to sufficient ultraviolet irradiation. However in countries with limited sunlight or where the population dresses in a fashion that reduces exposure to sunlight, the circulating levels of vitamin D metabolites are often low. This well explain why osteomalacia and rickets are common in Great Britain, Scandinavian countries, Middle East and India than in the United States.
To avoid rickets and osteomalacia, give plenty of milk to children and expose them to sunlight. Osteomalacia has been observed in 25 to 30% of bone biopsies among elderly patients who have suffered hip fracture in Scandinavia and Great Britain. Most likely this is because vitamin D intake and reduced sunlight exposure. Rickets among children are due to lack of vitamin D. Osteomalacia among the elderly is also due to lack of vitamin D. The prevention and cure of rickets by the formation of vitamin D through the skin by sunlight is of course firmly established.
Sunbathing has been advocated for keeping the cold away, developing immunity and robust health. Heat is soothing. When we take a sun bath it helps to relieve body pain and is relaxing. The effect of ultraviolet rays on common cold is well known. A group of subjects exposed to ultraviolet radiation reported about 40% lesser colds.
Sunbathing in olden times, was prescribed for tuberculosis. The beneficial effect was due to sunbathing and a general improvement in the regimen. After the manufacture of anti-tubercular drugs, generally a change of place or stay in a sanatorium for a few months is not prescribed. Sunbathing is liked by Westerners who on any sunny days take a holiday. All empty spaces and parks get filled with sunbathers.
The ultraviolet rays pass through the ozone layer of atmosphere its major portion gets absorbed. At mid day, when the sun is at ninety degrees it passes through much thinner layer of atmosphere and also thinner layer ozone. The content of ultraviolet rays is excessive and can cause sun burn. Before 8 a.m. or after 4 p.m. when the sun is at an angle it passes through a much thicker layer of atmosphere and ozone. So the content of ultraviolet rays is less and sufficient for body needs.
The ultraviolet rays are needed for the formation of vitamin D in the skin. The pro-vitamin D in the human skin is dehydrocholesterol, and it is converted to vitamin D by the help of ultraviolet rays. So sunbathing in the morning or evening hours just sufficient for the vitamin D formation and not sufficient to burn the skin. This is the right hour for sunbathing.
The sun’s rays when they pass through the window glass have most of its ultraviolet content absorbed. In winter, sunbathing can be enjoyed anytime of the day behind a window glass, thus avoiding bad effects of excessive ultra-violet rays. The soothing and relaxing effect of the sun is due to its heating effect.
We have a feeling of well being during sun bathing. Heat reduces pain in the body and relaxes muscles. This way you can also avoid the cold draft due to high velocity of wind. The effect of sunbathing will depend upon the clothing. White cloth reflects sunrays and so it has a cooling effect. If clothes are dark they absorb most of the heat and have a warming effect.