Hormones and your menstrual cycle: why it varies and what you can do
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Sometimes your period arrives like clockwork. Sometimes it skips a month, turns up late or changes character for no obvious reason. Hormones are in charge, but they are shaped in turn by everything from stress and sleep to what you eat. Here's what you need to know.
How do the hormones in your cycle work?
A normal menstrual cycle is 21 to 35 days long and runs on the interplay between four hormones: oestrogen, progesterone, LH and FSH. During the follicular phase, which starts on the first day of your period, oestrogen levels rise and prompt the ovary to prepare an egg.
Ovulation happens around the middle of the cycle, when LH suddenly spikes. After that, progesterone takes over and prepares the uterus for a possible pregnancy. If the egg isn't fertilised, hormone levels drop and your period starts.
Stress affects your cycle more than you think
Cortisol, the stress hormone, can disrupt the signals to your ovaries. During periods of high stress, ovulation can be delayed or skipped altogether, which makes your cycle irregular. It's your body's way of putting reproduction on hold when it senses a threat.
Over time, chronic stress can affect oestrogen and progesterone levels and contribute to PMS symptoms, heavier bleeding or irregular periods. Sleep plays a similar role: too little of it raises cortisol and throws your hormone balance off.
Diet, exercise and weight
Fat tissue produces oestrogen. Very low body fat, for example in elite athletes or with eating disorders, can cause periods to stop altogether, a condition called amenorrhoea. Conversely, being overweight can lead to excess oestrogen, which affects the cycle in a different way.
Intense exercise, especially without enough energy from food, can disrupt the hormonal axis that controls ovulation. Changes in diet and low iron or vitamin D are other factors many people underestimate.
When should you see a doctor?
An irregular cycle now and then is normal. But if your period has been missing for three months or more, if you have extremely heavy or painful bleeding, or if you suspect a hormonal imbalance, get a blood test and talk to a doctor.
Understanding your cycle is a powerful tool. Cycle-tracking apps like CLUE, Flo and Ovia can help you spot patterns and give you better notes to bring to your doctor's appointment.
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