Research in the last century has demonstrated that light is a critical regulator of physiology in animals. More recent research has exposed the influence of light on human behavior, including the phenomenon of seasonal affective disorder (SAD). Repeated studies have shown that light treatment is effective in this disorder. The molecular mechanism by which the body absorbs the light that has energizing and antidepressant effects is still uncertain. This review presents evidence regarding the role of rod and cone photoreceptors, as well as the role of recently discovered nonvisual neuronal melanopsin-containing photoreceptors. The authors discuss an evolutionary-based theoretical model of humoral phototransduction. This model postulates that tetrapyrrole pigments, including hemoglobin and bilirubin, are blood-borne photoreceptors, regulating gasotransmitters such as carbon monoxide when exposed to light in the eye. Recent studies in an animal model for seasonality provide data consistent with this model. Understanding the molecular mechanisms by which light affects physiology may guide the development of therapies for SAD and other pathologies of circadian and circannual regulation.
"At the other extremes, underexposure to sunlight can lead to deficiencies in vitamin D, thus increasing risks of heart disease , type 2 diabetes , and depression , as well as more well-known problems such as rickets . Underexposure to daylight can also have unhealthy consequences in seasonal affective disorders (SAD) suffered at extreme latitudes . "
[Show abstract][Hide abstract] ABSTRACT: The obesity epidemic and associated chronic diseases are often attributed to modern lifestyles. The term "lifestyle" however, ignores broader social, economic, and environmental determinants while inadvertently "blaming the victim." Seen more eclectically, lifestyle encompasses distal, medial, and proximal determinants. Hence any analysis of causality should include all these levels. The term "anthropogens," or "…man-made environments, their by-products and/or lifestyles encouraged by these, some of which may be detrimental to human health" provides a monocausal focus for chronic diseases similar to that which the germ theory afforded infectious diseases. Anthropogens have in common an ability to induce a form of chronic, low-level systemic inflammation ("metaflammation"). A review of anthropogens, based on inducers with a metaflammatory association, is conducted here, together with the evidence for each in connection with a number of chronic diseases. This suggests a broader view of lifestyle and a focus on determinants, rather than obesity and lifestyle per se as the specific causes of modern chronic disease. Under such an analysis, obesity is seen more as "a canary in a mineshaft" signaling problems in the broader environment, suggesting that population obesity management should be focused more upstream if chronic diseases are to be better managed.
[Show abstract][Hide abstract] ABSTRACT: Bright light therapy and the broader realm of chronotherapy remain underappreciated and underutilized, despite their empirical support. Efficacy extends beyond seasonal affective disorder and includes nonseasonal depression and sleep disorders, with emerging evidence for a role in treating attention-deficit/hyperactivity disorder, delirium, and dementia. A practical overview is offered, including key aspects of underlying biology, indications for treatment, parameters of treatment, adverse effects, and transformation of our relationship to light and darkness in contemporary life.
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