A fifteen-year-old athlete missing her period for three months is not a training milestone. It is a warning sign that a teenage athlete may have RED-S.
I see the aftermath of this in my clinic regularly, but I don’t see it early enough. By the time a young athlete reaches me, RED-S (Relative Energy Deficiency in Sport) has often been present for months, sometimes years, quietly affecting bone density at exactly the stage of life when bone mass should be at its highest rate of accrual. Adolescence is not just another life stage RED-S can affect. It is the stage where the cost of missing it is highest and the hardest to reverse.
What is RED-S in teenage athletes, and why does the timing matter so much?
RED-S occurs when an athlete’s body is not receiving enough fuel to cover both the demands of training and the basic requirements of everyday physiological function, including growth. In adults, the body deprioritises the reproductive system when that energy gap opens. In adolescents, it deprioritises more than that.
Roughly ninety per cent of adult bone mass is built by the late teenage years. That window does not reopen. An adolescent athlete training in an energy deficit isn’t just at risk of a missed period or two – she is at risk of never laying down the bone density she needs for the rest of her life, with consequences for fracture risk that can follow her well into adulthood. Growth and pubertal development can also be affected, sometimes resulting in delayed puberty or primary amenorrhoea (a period that never properly starts in the first place), which is easy to miss if nobody is asking the right questions.
This is the piece of youth sport menstrual health that I think gets least understood: in adults, RED-S is a health problem that can usually be reversed. In adolescents, some of what it affects cannot be undone.
The warning signs coaches and parents are best placed to see
Athletes at this age rarely raise these issues themselves, whether from embarrassment, not knowing what’s normal, or not wanting to be pulled from training. That makes coaches and parents, not clinicians, usually the first people in a position to notice something is off. What I’d want them watching for:
- A period that hasn’t started by fifteen, or one that starts and then stops for three months or more
- Recurring stress fractures, or bone stress injuries that keep coming back in different sites
- Growth or development that seems to be stalling compared to peers
- Fatigue that doesn’t improve with rest, or a performance plateau despite training consistently
- Getting ill more often than teammates on a similar programme
- Mood changes, low mood or increasing anxiety around food or training load
Why “she’ll grow out of it” is the wrong response
Missed periods in a young athlete get normalised more often than they get investigated. Sometimes that’s because heavy training genuinely can shift a cycle slightly, and it’s assumed this is simply more of the same. Sometimes it’s because nobody wants to be the person telling a promising fifteen-year-old that her training load needs to change. Both are understandable. Neither is safe to act on without proper assessment.
An adolescent athlete who is not getting a period is not operating on a hormonal profile that will simply correct itself once she’s a bit older or training slightly less. Left unaddressed, RED-S at this age can affect fertility later in life in ways that don’t surface until she’s trying to conceive, sometimes over a decade later, when the original cause has long been forgotten.
What I’d want every coach to do differently
If an athlete you coach hasn’t had a period by fifteen, or hers has stopped for three months or more, that’s worth a conversation and a referral, not a wait-and-see approach. The same goes for repeated stress fractures or a performance plateau that doesn’t respond to the usual adjustments. None of this requires you to diagnose anything. It requires you to notice, ask, and know that “it’s probably just training” is not a safe enough answer at this age.
If this resonates with you
If you coach or parent a young athlete and recognise any of this, it is worth seeking a proper assessment rather than waiting to see if things settle on their own. A thorough RED-S assessment looks at energy availability, training load, growth and pubertal development, and bone health together, not just whether a period eventually shows up.
I offer consultations in London, Windsor, and nationally and internationally via virtual appointments. You can book via this link HERE.
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