Human and animal activities, physiological processes, and behavior are subject to alterations caused by circadian rhythms, lunar cycles, and seasonal changes. Circadian  and seasonal rhythms [30,36] are well described, but the effects of the lunar cycle on humans and animals have been much less explored. The aim of this article was to review available data regarding effects of the lunar cycle on human and animal physiology, with particular attention paid to alterations in the immune response of experimental animals.
Fertility, menstruation, and births
The possibility of a lunar effect on the menstrual cycle was investigated in 312 university students . Of 312 women, 68 experienced lunar-period cycles (29.5 days). Forty-seven women of that group menstruated in the light half of the month; therefore, ovulation tended to occur in the dark phase of the lunar period, defined as the half cycle of the month from the last quarter through the new moon. Even women with irregular menses tended to ovulate during the dark phase of the lunar period. The author speculated that the lunar cycle is associated with the natural rhythm of electromagnetic radiation, which has an effect on the human menstrual cycle. In another study comprising 826 female volunteers  with normal menstrual cycles, a large proportion (28.3%) menstruated around the new moon, while at other times during the lunar month the proportions of menstruation were lower (8.8–12.6%) (p
Several reports describe the effects of the lunar cycle on the frequency of hospital admissions due to various causes. An infl uence of the lunar cycle was found in a two-year follow- up study of mortality due to cardiovascular emergencies (a total of 1,437 cases) . The periodicity was, in addition, affected by solar activity (spots, eruptions, etc). The maximum and minimum mortality curves shifted in their time phases so that during periods of high solar activity minimum mortality was nearer to the new-moon and full-moon phases, while maximum death rate approached the fi rst and last lunar quarters; during medium and low periods of solar activity the mortality maximums and minimums shifted counter-directionally to the moon’s orbit around the Earth. Others studied the incidence of acute coronary events and admission patterns in emergency medical and cardiology departments . Data from 1999 to 2001 were analyzed. Admissions on full-moon days were compared with those on new-moon days. There was increased incidence of acute coronary events associated with new-moon days (p=0.005). In another, prospective study, 447 consecutive patients with gastrointestinal hemorrhage were admitted over a period of two years . The admissions were allocated to their corresponding day of the lunar cycle, and full-moon and non-full-moon days were compared. The results of that study suggested an increase in the number of admissions during the full moon, especially in men and in patients experiencing variceal hemorrhage. However, the wide variation in the number of admissions throughout the lunar cycle could limit an interpretation of the results. Others analyzed 753 cases of acute infectious diarrhea in adults in 1981–1990 in Kosice . The group comprised 352 cases of bacillary dysentery, 305 patients with salmonellosis, 72 with campylobacteriosis, and 24 with yersiniosis. It appeared that statistically fewer patients were hospitalized (p