Frequently Asked Questions – Weight and Health

What does Body Mass Index mean?

Body Mass Index (BMI) is a ratio that can be used in deciding whether individuals and populations fall within a healthy weight range or not. It has been criticised because it does not reflect body muscle/fat ratios but nonetheless is more useful than weight alone. From a scientific point of view, women are ‘underweight’ with a BMI below 18.5. Having a BMI below 17.5 is one of the indications for a clinical diagnosis of anorexia nervosa.

BMI can be calculated by:
taking the weight in kilos e.g. 49
and dividing it by the height (in metres) squared
e.g. 1.64m x 1.64m = 2.69
49 ÷ 2.69 = 18.2

BMI doesn’t tell you anything about your body composition, and it is possible to be at a healthy weight and have either too little body fat or too little muscle to be healthy and able to stay strong for your dance work.

An adult (over the age of 18) with a BMI below 18.5  may be lacking muscle and/or body fat . For younger dancers there are charts which show the equivalent  values

Should I be worried if my periods stop?

Regular periods are a crucial marker for wellness. For dancers it is not unusual to miss one period, although this is not ideal. However, infrequent or absent periods, usually found together with low weight, will mean higher injury rates for the dancer, both muscular and skeletal (To et al., 1995), and slower healing times. If the periods stop altogether this is usually due to the dancer being very under weight (i.e. below a BMI of 17.5), although this varies, and many women need to be closer to a BMI of 20 to have normal periods, particularly if they are very lean. If the lack of periods continues beyond six months the impact on bone health may be irreversible. This is because oestrogen, a female sex hormone, plays a part in the development of healthy bones and its production is decreased when periods stop (Manual of Dietetic Practice, 2007). In women bone mass increases up until the age of around 30, but this increase is greatest before the 18th year. If the maximum bone mass is not achieved during this time, it is very difficult to make it up and if this is the case it can have consequences in later life; meaning an increased chance of developing osteoporosis (brittle bones).

Remember if you are taking the oral contraceptive pill ‘The Pill’, you will not be experiencing periods, just the effect of the changes in hormone levels when you have pill free days.

References

– Thomas, B & Bishop, J eds, 2007. Manual of Dietetic Practice, 4th Ed. Oxford: Blackwell.

– To, Wong & Chan, 1995. The effect of dance training on menstrual function in collegiate dancing students, Australian and New Zealand Journal of Obstetrics and Gynaecology, 35: 3: 304-309.
– Challis, J, 2004. If I have to weigh THAT much I’ll have to change career…, Dance UK News, Issue 52.

Images

– Mirriam-Webster, 2009. Skeleton [Diagram]. Available at: www.merriam-webster.com/art/med/skeleton.gif [Accessed 3 October 2009].

Weblink:
The National Osteoporosis Society: http://www.nos.org.uk