What we mean by periods stopping
Doctors use the word amenorrhoea for two situations. The first is a girl who has not started her periods at all by around 15, or within three years of her breasts starting to develop. The second is a girl whose periods were established and then stopped for three months or more.
Either version deserves a conversation with a GP. It is common in youth sport, and it is commonly waved away as part of being an athlete. It is not.
Why it happens in a healthy, hard-working teenager
The body treats a monthly cycle as optional. When the energy left after training is not enough to run everything, the reproductive system is one of the first things quietly turned down, ahead of anything the athlete would notice day to day.
That shortfall is usually accidental. Training goes up in September, a growth spurt raises the requirement, school lunch is at midday and training is at six, and nobody changes the food.
- Training load rising without food rising with it.
- A growth spurt increasing demand sharply for a year or more.
- Long gaps between meals on the busiest days.
- Deliberate restriction, sometimes driven by comments about physique.
- Illness, stress and short sleep stacked on top of a heavy schedule.
Why it matters beyond this season
Most of the bone your daughter will ever have is laid down in her teenage years, and the hormones behind her cycle are central to that process. Long stretches without periods during those years are linked with lower bone density and a higher chance of bone stress injuries such as stress fractures.
Some of that bone can be difficult to get back later, which is why this belongs in the same conversation as injury prevention rather than being filed under women's health.
The one line to remember
A missing period in a training teenager is information about her health, not a sign she is training well.
Other causes a GP will consider
This is exactly why the answer is an appointment rather than assuming it is the training. The assessment is straightforward and mostly a conversation plus blood tests.
- Polycystic ovary syndrome, which more often causes irregular rather than absent periods.
- Thyroid problems.
- Pregnancy, which will be asked about routinely and privately.
- Hormonal contraception, which can mask what her own cycle is doing.
- Rarely, other hormonal conditions that simple blood tests will pick up.
What to do this week
- Add food rather than removing sport: a real snack before training and a proper meal after it, every time.
- Put carbohydrate at every meal on training days.
- Look at the week honestly and cut any duplicated or low-value session.
- Protect eight to ten hours of sleep.
- Book the GP appointment, and mention training hours, growth and any injuries.
How to raise it with her
Keep it factual and unembarrassed. Something like: 'Your body needs more fuel than it is getting, and your cycle is one of the ways it tells us. Nothing is wrong with you and nothing needs to stop.' Framing it as fuel for performance, never as weight or diet, keeps the conversation open.
If food feels tense, secretive or rule-bound in any way, tell the GP that too. Early support is far easier than late support.