Running is a brilliant way to exercise – it strengthens your muscles, improves your fitness and focuses your mind. And the best thing is you can do it pretty much any time and anywhere. But of all the sports you can choose, runners are the most prone to something called exercise amenorrhea. That’s the scientific way of saying missed periods.

Those who train intensely (for an endurance race or marathon for example) tend to have very low body fat, as their ‘calories out’ outweigh their ‘calories in’. The combination of low weight (especially sudden weight loss) and intense exercise is what causes amenorrhea. Basically the body goes into starvation mode, and shuts down the processes that are not totally essential to survival.

Pro runners and passionate amateurs may find they occasionally miss a period. Some report this kicking in once they hit the 60+km a week, but it can start as low as 30km.

It’s not just a case of keeping the calories up. Amenorrhea can even happen to runners who eat well because those stress hormones that make you feel so good after a run also interfere with the brain’s production of the reproductive hormones that keep the menstrual cycle flowing.

So what? You might be thinking. Most of us probably don’t mind skipping a period here and there, and if you’re running regularly, well, it’s one less thing to worry about. But missing a period means you have not ovulated, and if you miss more than one period in a row, you're most likely going to be oestrogen-deficient. The health risks associated with that include infertility, thinning of the vaginal walls and breast tissue, osteoporosis and heart disease.

So what can you do? If this is sounding familiar, see your doctor straight away. Oestrogen levels can be boosted by birth control pills or HRT. But diet is the best way to get things back to normal naturally. Your GP will work with you on an eating plan that is full of protein, iron, zinc, iron and B6. You also need to make sure you are sleeping well and your body is recovering between sprints, so make sure you're giving your body and mind time to recover and relax.