the circadian clock . The circadian pacemaker , the master clock is in the suprachiasmatic nucleus of the hypothalamus . The retinohypothalamic pathway synchronizes biological rhythms with the earth ’ s day / night cycle . Timely exposure to sunlight or artificial light with similar spectrum can be used to treat circadian rhythm disorders like the delayed or advanced sleep phase syndrome . Another major benefit is the effect of sun on the mood . Serotonin levels are affected by exposure to light and higher serotonin levels are correlated with more positive mood and a calm yet focused mental outlook . 1 A classic example of mood disorder related to sunlight is seasonable affective disorder ( SAD ), a type of depression that sets in when the days get shorter and shorter . This is a recurrent problem during the winter . The reciprocal effect of sunlight mediated through serotonin and melatonin which normally occurs during sleep wake cycle is disrupted in SAD . Use of light therapy ( to compensate for the decreased amount of sunshine during winter ) has been an effective treatment .
The story of the use of sunlight for treatment of neonatal jaundice ( heliotherapy ) is a testament to the importance of astute observation in medical discoveries . A nurse in the Premature Unit at the Rochford general hospital in Essex , England , Sister Jean Ward in the year 1956 made the serendipitous observation that exposure to sunlight reduced the skin discoloration from jaundice . Eventually it became clear that visible light in the blue-green spectrum with wavelength of 430-490 nm can convert unconjugated bilirubin to water-soluble isomers , which can be eliminated from the body . Sister Ward ’ s initial discovery later led to the use of phototherapy for neonatal jaundice and saved many babies from developing bilirubin encephalopathy .
Now that we have delved into the Good of the sun , it is time to look at the Bad side of the Helios . Sunburn is perhaps the most common undesirable effect of exposure to UV radiation from the sun . Sunburn can potentially lead to premature aging of skin and skin cancer . The underlying mechanism is considered to be damage to DNA and suppression of the immune system . Photodermatoses can be induced or exacerbated by exposure to the sun ’ s UV radiation and the potential for certain drugs to induce photosensitivity is a well-known hazard . Yet another bad effect of UV radiation is its potential to induce cataract . It has been estimated that the implementation of the Montreal protocol to control ozone-depleting substances ( leading to lessening of sun ’ s UV rays reaching the earth ) can effectively cut down on the incidence of cataracts significantly . 2
Let us look at some of the less well-known bad effects of sunshine . Being a clinician , I cannot resist the temptation to describe one of my patients I saw decades ago , who presented with a unique clinical picture . I was newly on the Neurology faculty and was given the task of organizing a clinic for epilepsy patients . This provided an opportunity to see a very large number of epileptic patients , many with mundane and some with unique semiology . Frustrated and concerned parents brought their 12 year old son with an unusual problem . He exhibited a tendency to run out when the sun was bright , stare at the sun and wave his hand repeatedly in front of his eyes ; after a few seconds he will develop jerky movements of his hands and fall and sometimes develop a generalized tonic-clonic seizure . The parents tried to admonish and even confine the kid to indoors while the sun was out , with no success . I realized that this was like the seizures induced by stroboscopes or during a similar situation while driving along a tree-lined street with sunlight from the side . The patient did show photosensitivity based on presence of photoparoxysmal response in the EEG during stimulation with photic flashes . However , self-induction of seizures with heliotropism ( attraction to the sun ) was new to me . It was an era prior to PubMed and Google Scholar , and a protracted and time-consuming search in the medical library detected only a single report of self-induced seizure . I was able to see nine more similar patients over the next 10-year period . These cases were reported with the caption “ heliotaxic ” epilepsy . 3 The condition currently has a more apt name “ sunflower syndrome ” denoting head movement of these patients to face the sun directly . 4
The Ugly side of Helios must deal with the skin cancer hazards . Apart from sunburn , UVB radiation also causes generation of DNA-damaging molecules and oncogenesis . Melanoma , basal cell carcinoma and squamous cell carcinoma have all been linked to exposure to ultraviolet radiation from the sun . Exposure of skin to the sun ’ s UV radiation is considered the primary modifiable cause of skin cancer . Australia was one of the first countries to initiate programs ( in the early 1980s ) to mitigate UV radiation effects , the Slip-Slop-Slap initiative (“ slip on a shirt , slop on sunscreen and slap on a hat ”). This initiative of 1981 followed by the SunSmart program has apparently resulted in a decrease in melanoma incidence in the younger age group in Australia . 5
I will conclude with a quote from Anthony Liccione : “ The Sun can be your greatest gloom or your greatest comforter , depending on how you view its shine .”
References :
1
Mead MN . Benefits of sunlight : A bright spot for human health . Environ Health Perspect . 2008 116 ( 4 ): A160-A167
2
Neale RE et al . The effects of exposure to solar radiation on human health . Photocem Photobiol Sci . 2023 22 1011-1047
3
Iyer VG . et al . Heliotaxic epilepsy . JAPI 1983 31 ( 5 ) 284-285
4
Ames FR , Saffer D The Sunflower syndrome : A new look at “ self-induced ” photosensitive epilepsy . J Neurol Sc 1983 59 ( 1 ). 1-11
5
Walker H et al . Forty years of Slip ! Slop ! Slap ! A call to action on skin cancer prevention in Australia . Public Health Res Pract . 2022 ; 232 ( 1 ): e31452117
Dr . Iyer practices at the Neurodiagnostic Center of Louisville and is a retired professor f neurology at the University of Louisville School of Medicine .
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