Infradian Rhythms

• Infradian rhythms occur over a longer period of than 24 hour.
• The human female menstral cycle has an average of 28 days less than one cycle in 24 hours. Rising levels of oestrogen cause the ovary to release an egg (ovulation). Then progesterone helps the womb lining to thicken, readying the womb for pregnancy.

  If pregnancy doesn't occur , the egg is absorbed and the womb lining comes away.
• Stern & McClintock Pheromone study

  Stern & McClintock studied 29 women with irregular periods. Pheromones were taken from 9 at different stages of their cycles, via a cotton pad under their armpits. These pads were cleaned with alcohol and later rubbed on the upper lips of the 20 women. 68% of women experienced changes to their cycle which correlated to that of their odour donor.
• Seasonal affective disorder (SAD)

  SAD is a depressive disorder with a seasonal pattern. Its often called the winter blues; the symptoms are triggered during the winter months when the number of daylight hours becomes shorter. During the night, the pineal gland secretes melatonin until dawn when there is an increase in light. In winter, less light means secretion goes on for longer. This has a knock-on effect on the production of serotonin in the brain. Low serotonin is linked to depressive symptoms.