Could visible light contribute to the development of leukaemia and other cancers in children?

Nocturnal light pollution and underexposure to daytime sunlight: Complementary mechanisms of circadian disruption and related diseases

Routine exposure to artificial light at night (ALAN) in work, home, and community settings is linked with increased risk of breast and prostate cancer (BC, PC) in normally sighted women and men, the hypothesized biological rhythm mechanisms being frequent nocturnal melatonin synthesis suppression, circadian time structure (CTS) desynchronization, and sleep/wake cycle disruption with sleep deprivation. ALAN-induced perturbation of the CTS melatonin synchronizer signal is communicated maternally at the very onset of life and after birth via breast or artificial formula feedings. Nighttime use of personal computers, mobile phones, electronic tablets, televisions, and the like--now epidemic in adolescents and adults and highly prevalent in pre-school and school-aged children--is a new source of ALAN. However, ALAN exposure occurs concomitantly with almost complete absence of daytime sunlight, whose blue-violet (446-484 nm λ) spectrum synchronizes the CTS and whose UV-B (290-315 nm λ) spectrum stimulates vitamin D synthesis. Under natural conditions and clear skies, day/night and annual cycles of UV-B irradiation drive corresponding periodicities in vitamin D synthesis and numerous bioprocesses regulated by active metabolites augment and strengthen the biological time structure. Vitamin D insufficiency and deficiency are widespread in children and adults in developed and developing countries as a consequence of inadequate sunlight exposure. Past epidemiologic studies have focused either on exposure to too little daytime UV-B or too much ALAN, respectively, on vitamin D deficiency/insufficiency or melatonin suppression in relation to risk of cancer and other, e.g., psychiatric, hypertensive, cardiac, and vascular, so-called, diseases of civilization. The observed elevated incidence of medical conditions the two are alleged to influence through many complementary bioprocesses of cells, tissues, and organs led us to examine effects of the totality of the artificial light environment in which humans reside today. Never have chronobiologic or epidemiologic investigations comprehensively researched the potentially deleterious consequences of the combination of suppressed vitamin D plus melatonin synthesis due to life in today's man-made artificial light environment, which in our opinion is long overdue.

Chemotherapy and dietary phytochemical agents

Chemotherapy has been used for cancer treatment already for almost 70 years by targeting the proliferation potential and metastasising ability of tumour cells. Despite the progress made in the development of potent chemotherapy drugs, their toxicity to normal tissues and adverse side effects in multiple organ systems as well as drug resistance have remained the major obstacles for the successful clinical use. Cytotoxic agents decrease considerably the quality of life of cancer patients manifesting as acute complaints and impacting the life of survivors also for years after the treatment. Toxicity often limits the usefulness of anticancer agents being also the reason why many patients discontinue the treatment. The nutritional approach may be the means of helping to raise cancer therapy to a new level of success as supplementing or supporting the body with natural phytochemicals cannot only reduce adverse side effects but improve also the effectiveness of chemotherapeutics. Various plant-derived compounds improve the efficiency of cytotoxic agents, decrease their resistance, lower and alleviate toxic side effects, reduce the risk of tumour lysis syndrome, and detoxify the body of chemotherapeutics. The personalised approach using various phytochemicals provides thus a new dimension to the standard cancer therapy for improving its outcome in a complex and complementary way.

What do we know 40 years after Nixon declared the 'war on cancer'? On the origin, prevention and treatment of cancer

Evolutionary principles suggested by Darwin and Wallace some 150 years ago can provide insights into the origins of cancer. Moreover, they can form a basis for answering the question implicitly posed when Nixon declared the war on cancer in 1971: Can we actually 'cure' cancer? As explained lucidly by Greaves in 2001, necessary keys to evolution and thus for the origin of species, including ours, are changes of genes or mutations; but changes of genes are also necessary links in the causal chains which lead to cancer. In effect, cancer is therefore, according to Greaves, an 'evolutionary legacy'. Intriguingly, the realization that cancer is a consequence of changes in genes which are conditiones sine qua non for evolution suggests a mutation paradox on an evolutionary scale: in individuals, mutations may have devastating adverse health effects, including cancer. Populations, however, as a whole can be expected to benefit ultimately from changes of genes to better adapt to environmental challenges. On the basis of premises from evolution theory, it remains for us to interweave growing insights into evolutionary principles with realistic objectives for the primary prevention of and, where the latter fails, coexistence with cancer so that what we do for patients can become more of an art rather than a war.

Indirect blue light does not suppress nocturnal salivary melatonin in humans in an automobile setting

In 2007, the International Agency for Research on Cancer (IARC) classified shift work that involves circadian disruption as being probably carcinogenic to humans (Group 2A). In this context, light exposure during the night plays a key role because it can suppress nocturnal melatonin levels when exposures exceed a certain threshold. Blue light around 464 nm is most effective in suppressing melatonin because of the spectral sensitivity of melanopsin, a recently discovered photopigment in retinal ganglion cells; the axons of these cells project to the suprachiasmatic nucleus, a circadian master clock in the brain. Due to advances in light technologies, normal tungsten light bulbs are being replaced by light-emitting diodes which produce quasi-monochromatic or white light. The objective of this study was to assess whether the light-melanopsin-melatonin axis might be affected in automobiles at night which employ the new generation diodes. To this end, we have tested in an experimental automobile setting whether indirect blue light (lambda(max) = 465 nm) at an intensity of 0.22 or 1.25 lx can suppress salivary melatonin levels in 12 male volunteers (age range 17-27 years) who served as their own controls. Daytime levels were low (2.7 +/- 0.5 pg/mL), and night-time levels without light exposure were high (14.5 +/- 1.1 pg/mL), as expected. Low-intensity light exposures had no significant effect on melatonin levels (0.22 lx: 17.2 +/- 2.8 pg/mL; P > 0.05; 1.25 lx: 12.6 +/- 2.0 pg/mL; P > 0.05). It is concluded that indirect blue light exposures in automobiles up to 1.25 lx do not cause unintentional chronodisruption via melatonin suppression.

Light Hygiene: Time to make preventive use of insights--old and new--into the nexus of the drug light, melatonin, clocks, chronodisruption and public health

Light is, clearly, a key to life on Earth and light, equally clearly, determines biological rhythmicity in organisms. Light does the latter by setting internal or endogenous clocks which allow a multitude of species, including man, to adjust their lives to changing external or environmental conditions. Critical changes over time occur from day to night and throughout the year. In this paper, we sum up how visible light provides electromagnetic information about environmental "time" via the ocular interface of newly discovered photoreceptive cells to a master clock in our brain, viz the suprachiasmatic nuclei [SCN], and how the SCN translate this input, with melatonin as a key biologic intermediary, into endogenous or biological time. We summarize experimental and epidemiological evidence suggesting how chronodisruption, a relevant disturbance of the temporal organization or order of physiology, endocrinology, metabolism and behaviour, is probably detrimental for human beings. On the basis of our synthesis, and in line with suggestions by other researchers voiced decades ago, light must, functionally, be considered as a drug equivalent. In this vein, the very timing, quality (wavelength), quantity (dose) and side effects, including chronodisruption, of light exposures can be critically important for health and disease in man. As a promising means to foster public health, we advocate an appropriate balance of exposures to the key Zeitgeber light in terms of "light hygiene", implying strong and appropriate rather than weak and confusing temporal information. This focus on "light hygiene", and thus on the key Zeitgeber light, does not mean to ignore that there are multiple entrainment pathways for our circadian clocks. Indeed, when dealing with light, chronodisruption and a multitude of adverse health effects, we ultimately need to consider Zeitgeber cues, and their possible interplay, beyond light alone. Confusions of the temporal programmes in humans can also stem from physical and social activities, stress and facets of food intake. And yet, since light possesses a rather unique and exclusive Zeitgeber role and in view of its ubiquitous nature, a specific, preventative focus on "light hygiene", as a contribution to a general "Zeitgeber hygiene", is warranted.

Defining chronodisruption

When the International Agency for Research on Cancer (IARC) classified shift-work that involves circadian disruption as probably carcinogenic to humans in 2007, this was the prelude to extensive experimental and epidemiological research in coming years. Indeed, with some 20% of people worldwide being engaged in some type of work at unusual times, including the night, it is a must to investigate, and to clarify as soon as possible, the biologically plausible links via circadian disruption with epidemic cancers such as of the breast or prostate. Surprisingly, neither the IARC information available so far nor the general literature provides a clear definition of what the critical component in the postulated chain of causation, namely circadian disruption, is. Here we offer our definition of chronodisruption (CD), a concept which we proposed in 2003 and which we operationalized recently in research which addressed the putative links between shift-work, time-zone-travel and human cancers independently of the IARC and led to similar causal interpretations. As a basis for further research in this area with possible high relevance for public health, we: (i) elaborate our definition of CD, with melatonin being a key biological intermediary, by putting critical disruptions, and the resulting disorder, of circadian clocks, biological rhythms and circadian organization into thematic and historical context with Colin Pittendrigh's insights almost half a century ago; (ii) provide material on 'what are chronodisruptors?' and (iii) pose a key question which needs to be answered by and for experimental and epidemiological CD research. We hope that defining CD can contribute to studies which may help to find clues to a background incidence of epidemic internal cancers for which--so far in many cases--we lack causal explanations.