Why 'the curse' is often lifted for female athletes
Absence or cessation of menstrual periods - technically known as amenorrhoea - is a common problem among sportswomen competing at high levels in any physically demanding sport, whether it be running, swimming, cycling, martial arts or tennis.
Intense training of any kind places immense strains on many of the body's systems. Physical and mental processes that regulate human biological function can be disrupted and may then take the body on a journey it was never designed for. One system, which is prone to disruption - in women, at least - is the reproductive one. And when that happens the first sign is usually interference with normal menstruation.
However, I want to stress at the outset that this sort of problem is not an inevitable consequence of strenuous exercise and that reproductive health can be maintained if you know how far to push your body.
The first menstrual period of an adolescent girl is known as the menarche. Studies have proven that intense exercise can delay the onset of menarche by disrupting the hormonal patterns that controlmenstruation. A girl who has not reached menarche by age 15 would be considered abnormal by most doctors. But this does not necessarily imply that she has a medical problem. She may be a late starter for genetic reasons. Or it could be that her exercise habit has kept her body fat levels below what is needed to trigger menstruation.
A young woman who has never menstruated has what is known as primary amenorrhoea. Girls over 15 with this condition should always be seen by a doctor to rule out any medical abnormalities.
Women who have reached menarche and had normal periods, which are subsequently interrupted, have what is known as secondary amenorrhoea - a condition that is very common among female athletes from all disciplines. Research suggests that between 5% and 20% of female track athletes suffer from secondary amenorrhoea. By contrast, it affects only 2-3% of non-athletic women - usually caused by illness or emotional stress.
Exercise is only one side of the coin
Intensive exercise has been blamed for secondary amenorrhoea - but it is only one side of the coin. The onset and maintenance of menstruation is controlled by a regulating factor released by the hypothalamus in the brain, known as gonadotrophin-releasing hormone (GnRH). Other factors that affect this highly complex system are stress, body weight and body composition. The main relevant factor in body composition is the percentage of body fat. Providing a woman maintains her body fat levels, strenuous exercise can be taken without compromising normal menstruation. Conversely, a woman who takes no exercise yet has very low body fat levels - an anorexic, for example - is very likely to experience disrupted menstruation.
Thus, all women need to be aware of three key factors: exercise, stress and body fat levels, which interact with each other to determine menstrual status.
It can be difficult to disentangle stress from the other factors: the pressures associated with dieting, competing or juggling heavy training loads with busy lives can disrupt menstruation as much as exam stress or the death of a loved one. Many amenorrhoeal athletes resume normal menstruation as soon as the competitive season ends; release from the tension of preparation for competition may be all it takes to normalise their menstrual patterns.
As far as body fat is concerned, how much is enough? Athletes who train themselves into levels of low body fat for periods of more than three months usually suffer from secondary amenorrhoea, which occurs, on average, when fat levels fall below 20%. However, athletes with fat levels between 20 and 25% are likely to experience an intermediate problem known as oligomenorrhoea, when periods are occasional rather than regular.
Body-builders and long-distance runners sometimes reduce their fat levels to as low as 12-17% - and some go even lower for major events! Such athletes are combining all the risk factors for amenorrhoea, making it very likely that their periods will stop.
Fit women have healthier babies
The good news is, though, that exercise-induced amenorrhoea, whether primary or secondary, is normally reversible, with most women resuming regular menstruation within three months of easing their training load and/or gaining weight. Fertility rates of former athletes are no lower than average - and physically fit women tend to have easier labours and healthier babies.
However, the longer the periods are absent the greater the risk that additional medical complications will be superimposed on the original problem. A woman who has not menstruated for six months or more has chronic amenorrhoea, which can be serious as it is linked with accelerated bone deterioration. The reason for this link is not entirely clear, but one theory is that the low blood oestrogen levels associated with amenorrhoea lead to heightened sensitivity of the bone to parathyroid hormone, which controls blood levels of calcium, an important constituent of bones. The consequent increase in blood calcium levels suppresses parathyroid hormone secretion and this, in turn, impairs conversion of vitamin D to its active form, reducing the body's capacity to absorb calcium.
Difficult though it is to grasp, this theory goes some way to explaining why attempts to compensate for this bone mineral loss by increasing dietary intake of calcium do not appear to work. In addition, some evidence suggests that the increased blood calcium levels caused by low levels of oestrogen speed up the rate of calcium excretion in the urine. Thus chronic amenorrhoea gives rise to a double whammy, in which the body minimises its absorption of calcium while maximising its excretion.
Of course, it must be emphasised that all women are unique and their bodies will react differently to the same stressors. It would therefore be unwise to indulge in sweeping generalisations and hard and fast recommendations. Every woman affected by amenorrhea needs to examine her own lifestyle and training habits in the light of the issues raised by this article.
It is clear that fast weight loss and heavy training loads will almost certainly contribute to either primary or secondary amenorrhoea. But it is also clear that female athletes can indulge in strenuous exercise without risk, as long as normal menstrual function is maintained at least some of the time. Women should never be discouraged from training or competing at a high level because of the potential effects on their menstrual function. Nevertheless, they should be aware of potential problems and give their bodies a chance to recover whenever possible. The best advice I can offer all athletes - male and female - is, listen to your body, and train safely and intelligently.
Carl Fisher