Infradian Rhythms

• Across 28 days, the amounts of Oestrogen and Progesterone released into the bloodstream varies. Oestrogen release peaks halfway through the cycle on day 14 whereas progesterone peaks on day 21 of the cycle
• Oestrogen and progesterone are the two main hormones associated with the menstrual cycle and are responsible for controlling the release of the egg from a woman's ovaries (ovulation)
• Every month an egg is released on day 14 which is when oestrogen is at its peak. Then progesterone levels increase to allow the egg to be fertilised by the sperm if present. If the egg isn't fertilised it breaks down and the drop in progesterone at the end of the cycle signals a woman's period
• A biological rhythm with a cycle that lasts more than 24 hours is called an Infradian rhythm
• An example of an Infradian rhythm is Seasonal affective disorder (SAD) which affects a person's mood. It is when people experience low mood during winter and better mood during summer. This follows a cycle which repeats every year