I'm glad to hear that you've managed to get back to a healthy weight after what was clearly a very difficult time for you, and I hope that all your stress is now under control.

It's very likely that your periods will return although it's not possible to say how soon.

The disappearance of menstrual periods is a common problem with extreme weight loss. Many girls with anorexia find their periods stop, quite often even before much weight has been lost (in fact, lack of periods is one of the features essential to make a diagnosis of this condition). Younger anorexics may never even start their periods.

Hormonal chaos is to blame

The explanation of these disturbances is complex because it involves the interaction of a number of different hormones, which are controlled by an area of the brain called the hypothalamus and influenced by many other factors, including some external ones like emotional stress and shock.

One of the main controlling hormones released by the hypothalamus is called gonadotrophic releasing hormone or GnRH. This hormone is released in pulses throughout the day, starting when a girl begins to grow rapidly in the three to four years before her periods start. When she reaches a critical weight, or more accurately when the proportion of fat in her body exceeds a critical level, her first period starts.

When the body weight falls below a certain level, the hypothalamus fails to release pulses of GnRH, the ovaries aren't stimulated to release eggs and periods stop. This usually happens at a body mass index (BMI) of about 17.5, or a body weight roughly 80 per cent of average body weight.

If body weight increases above the critical level then the whole system gets going again. So periods will restart, but there's often a delay for the hormonal system to get fully into action and many girls like you will find that it'll be some months before their periods start.

Exercise can delay periods

Excessive exercise can also stop the pulsatile release of GnRH. If a girl's weight is below normal but above the critical level, exercise may be enough to prevent periods from occurring. This is a common problem with ballet dancers.

At 8 and a half stone, you're unlikely to be very underweight even if you're quite tall. To check how normal your weight is you need to find out your BMI, which involves knowing your weight AND height. You can do this at : bbc.co.uk/health/healthy_living/your_weight/bmiimperial_index.shtml

Be patient

Your periods should return fairly soon, especially as your weight loss wasn't a very long-term problem. However, some women find their periods don't return for months or even years after returning to a normal weight, and the explanation for this isn't totally clear. Ongoing emotional stress may play a part.

• Be as patient as you can.
• Try not to overdo any exercise.
• Don't forget contraception if you're having sex. Some women have become pregnant despite a low body weight and having had no periods for years.
• If you're still concerned talk to your doctor, who may want to do a few simple checks.

This article was last medically reviewed by Dr Trisha Macnair in June 2008