Light exposure during the night is becoming progressively more common throughout the world, particularly in areas where electricity is commonly used. Also, the availability of artificial light has allowed humans to work or recreate throughout the 24-hour day. Based on photographs taken of the Earth from outer space, it is also apparent that true darkness is disappearing. For years it was assumed that polluting the daily dark period with light was inconsequential in terms of animal/human physiology. That assumption, however, has proven incorrect. Light at night has two major physiological actions, i.e., it disrupts circadian rhythms and suppresses the production of melatonin by the pineal gland. Moreover, both these changes are light intensity and wavelength dependent. Both human epidemiological and experimental studies on animals have documented that a potential negative consequence of chronodisruption and nocturnal melatonin inhibition is cancer initiation and growth. In epidemiological studies, the frequency of each of the following cancers has been reportedly increased in individuals who routinely work at night or whose circadian rhythms are disrupted for other reasons (e.g., due to jet lag): breast, prostate, endometrial, and colorectal. Likewise, in experimental animals, cancer growth is exaggerated when the animals are repeatedly phase advanced (as occurs during easterly flights) or exposed to light at night. A variety of mechanisms have been examined to explain how the suppression of melatonin exaggerates cancer risk. Mechanistically, how chronodisruption (without a consideration of melatonin suppression) would enhance cancer frequency is less clear. In addition to cancer, there may be other diseases that result from the chronic suppression of melatonin by light at night.

We have examined data from 12 epidemiologic studies for quantitative evidence of biologic synergy between asbestos and smoking on lung cancer risks. Estimates of the effect associated with joint exposure to the two agents exceeded the sum of their separate effects in each study. We explored the variations in the strength of the synergistic effect across the studies using three indices: the ratio of the combined effects to the sum of the separate effects of smoking and asbestos (S), the relative excess risk due to interaction (RERI), and the attributable proportion of risk due to interaction (AP). The weighted average of S across all studies was 1.64 (95% confidence interval = 1.33-2.03). The attributable proportion associated with this average S was estimated as 33%, that suggests that one-third of cancer cases among smokers who were exposed to asbestos can be attributed to the synergistic behavior of the two carcinogens, as distinct from their separate effects and those attributable to other ("background") factors.

Successful finishing of marathon requires regular endurance training and appropriate lifestyle. Thus, marathon running times and training data from large samples of physically active and fit elderly are ideal for the assessment of age-related performance. In the present study we analyzed 439 278 running times from result lists of 108 marathon competitions and data from a survey via internet questionnaire about training and behavioural factors of marathon finishers. Marathon times and 6 992 data sets from the internet questionnaire were separated into groups based on age and sex and analyzed by two-way ANOVA. Our main findings are that 1) there are virtually no relevant running time differences (p<0.01) in marathon finishers from 20 to 55 years and 2) the majority of middle-aged and elderly athletes have training histories of less than seven years of running. With the exception of marathon running times we did not encounter any significant gender related differences (p>0.01). The present findings strengthen the concept that considers aging as a biological process that can be considerably speeded up or slowed down by multiple lifestyle related factors.

Research into health effects of chronodisruption (CD), a relevant disturbance of the circadian organization of physiology, endocrinology, metabolism and behaviour, is evolving at a rapid pace. With regard to malignancies, our synthesis of key experiments indicates that CD can play a causal role for cancer growth and tumor progression in animals. Moreover, our meta-analyses of 30 epidemiological studies evince that flight personnel and shift workers exposed to chronodisruption may have increased breast and prostate cancer risks: summary relative risks (RRs) for investigations of flight personnel and of shift workers suggested a 70 and 40% increase in the risk of breast cancer, respectively, and excess relative risks of prostate cancer in nine studies in flight personnel (40%) and in two studies in male shift workers. There was a remarkable indication of homogeneity of results from the individual studies that contribute to the average statistics. However, in view of doubts about whether the differing assessments of CD can really be regarded as valid reflections of the same causative phenomenon and the lack of control of covariates in the majority of studies, it is premature to conclude that the risk observations reflect a real, rather than spurious, association with CD. The challenge for future epidemiological investigations of the biologically plausible links between chronodisruption and human cancers is to conduct studies which appreciate details of transmeridian travelling, of shift work and of covariates for the development of the diseases.

Few studies have investigated the association between body mass index and fecundability, that is, the ability to conceive in a menstrual cycle, among fertile women with normal menstrual cycle pattern. We examined the independent and combined effects of duration and regularity of the menstrual cycle, body mass index, and fecundability from records on pregnant women attending antenatal care at Odense University Hospital, Denmark, between 1972 and 1987. We included only the first birth of each woman who had planned pregnancies and no pre-pregnancy disease (N = 10,903). We estimated the fecundability odds ratio (FR) as the odds of conception in a menstrual cycle. After adjusting for confounders, the fecundability for women with a body mass index >25 kg/m2 was lower than for women with a body mass index of 20-25 kg/m2 [FR = 0.77; 95% confidence interval (CI) = 0.70-0.84]. FR was lower for women with long (>35 days) (FR = 0.74; 95% CI = 0.63-0.87) or irregular cycles (FR = 0.78; 95% CI = 0.70-0.87), even when their body mass index was within the normal range (20-25 kg/m2) and/or their cycles were regular.