Sunshine, the eternal provider, is found to be protector too, says S.Ananthanarayanan.
The earth’s ecosystem is a complex of adaptation to use the energy that we receive from the sun. While physical features, mountains, oceans, the seasons, have settled into a rhythm, following physical laws, the earth’s vegetation has evolved to capture and store the sun’s energy. The diversity of the animal kingdom has then organised itself to exploit, directly or indirectly, these plant and vegetable resources.
Animals, however, also bypass the plant intermediary and sometimes use the sun’s bounty by themselves. A simplest instance is in the use of light for vision. A more specialised one is the absorption of sunlight energy by the skin of animals to become the power source for synthesis, primarily of Vitamin D. Yet another instance has now emerged, of supporting the immune system, and this has been detailed in the Nature group journal, Scientific Reports, by Thieu X. Phan, Barbara Jaruga, Sandeep C. Pingle, Bidhan C. Bandyopadhyay and Gerard P. Ahern, of the Georgetown University and the Veteran Affairs Medical Centre, both in Washington, and the Department of Biology, Vinh University, Vietnam.
The role of sunlight in the synthesis of Vit D is well known. It is the ultra violet part of the spectrum, in sunlight, that is effective. It is hence not the warmth of sunlight, even if we are in the open, but fully clothed, nor even taking sunlight on the skin behind a glass window, which blocks the ultra violet, that is useful. We need direct sunlight, preferably midday, and on the skin. Rays from the slanting sun during winter months in the northern countries, for instance, are not useful, which is why people in those countries rush to the beaches in the summer.
The manufacture of Vit D happens in the inner parts of the thin, outer layer of the skin, the epidermis. Near ultra violet, or light only a little past the blue side of the visible spectrum, is able to penetrate to this part of the skin. These photons are a little more energetic than those of visible light and they convert 7-dehydrocholesterol, a form of cholesterol, a major component of the body cells, into a precursor of Vit D, which changes to Vit D within about a day. There is ample supply of cholesterol and a short exposure to bright sunlight is all it takes to for a person to generate a day’s requirement of Vit D. Vit D then plays an important role in the body, by enabling the absorption of calcium and strengthening the bones and similarly several other processes, including the immune system.
While plants generally do not produce Vit D, the earliest source was phytoplankton in the sea, over 500 million years ago. This was the source of Vit D for early, ocean bound vertebrates, but land based animals needed their own source to sustain their calcium-rich skeletal structure. Vit D synthesis using sunlight has hence been around since 350 million years.
Another role
What the Washington and Vietnam based group has discovered is yet another role of parts of sunlight that get past the outer layer of the skin. The layer just below the epidermis, called the dermis, is rich in T cells, which are an important part of the immune response of the body. T cells are abundant in the skin, which contains, in fact, twice the number of T cells in circulation in the blood stream. This may be just as it should be, as the skin the body’s largest organ and the gateway used by myriads of microbes. T cells are either ‘helper’ T cells, which enable the action of other parts of the immune system, or they are ‘killer’ T cells, which destroy virus infected or tumorous cells. And then there are memory T cells, which persist with a record of specific antigens even after a first attack has been overcome.
What the researchers have discovered is that sunlight which gets through to T cells has the effect of increasing the motility, or the movement, of T cells. As T cells, which act against infection, need to move to the site of infection, an increase in their capacity to move is an increase in their capacity to maintain body immunity. While the epidermis is opaque to ultra violet light, blue light, which is the part of the spectrum just below ultra violet, in energy, is able to get through and reach the part that is rich in T cells. The Scientific Reports paper notes that blue light passes through the dermis and is reflected back by the blood vessels, so that the inner layer of the skin is doubly bathed in blue light. This apart, the study notes, that T cells in the dermis are affected by blue light amounts to the discovery of a new type of photosensitive cell, apart from the rods and cones of the eye!
The researchers found that T cells contain the same components that are found in the cells of the retina, which are light sensitive. Laboratory trials with T cells then showed that the cells were sensitive to UV and blue light, responding with generation of hydrogen peroxide, which leads to higher levels of calcium ions, which are important carriers of signals within and between cells. It is the change of calcium ion concentration that brings about contraction of muscles, and in T cells, irradiation with blue light led to changes in shape and increased and faster random movements of the cells. Hydrogen peroxide is also the substance that white blood corpuscles release to trigger immune response when they sense infection. “It all fits together,”, Gerard P Ahern, from Georgetown University is reported to have said.
Exposure to sunlight is already celebrated for production of Vit D, and to be more effective than the use of dietary supplements. What we now have is the mechanism by which sunlight promotes the immune reaction of the body, and one more reason for each one of us to go out in the sun. There is a great deal of needless suffering and health care expense that could be avoided if people systematically made sure that they get a short, daily dose of sunshine – with just some changes in lifestyle and maybe social mores.
The wonDer vitamin
Not getting enough Vit D is implicated in many medical conditions: depression, asthma, high blood pressure and heart disease, diabetes, bowel disease, MS, arthritis, cancer, flu, TB, and then muscle and bone ailments. The only dietary sources are fish, milk and eggs and even when derived from these, the vitamin needs to be converted into a useful form by the liver cells. In contrast, Vit D that is produced by the skin, when bathed in sunlight, is abundant and also more readily processed in the liver.
A first casualty of Vit D deficiency is the skeletal frame – rickets and osteoporosis. Deficiency can be treated with injections and oral supplements, tablets and sachets, taken for a few months. But twenty minutes in direct sunlight, with as much of the skin exposed as possible, would be quicker and more effective, and cheaper. The benefits would be general increase in vitality and saving the cost of treating fractures, especially in the aged, apart from the cost of the care giver and working days lost.
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