Diabetes complications
Diabetes complications

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Diabetes complications

6 Calculating body mass index

Being overweight is another risk factor for CHD, as well as a risk factor for developing Type 2 diabetes. Assessing whether somebody is overweight can be done in two ways. Simply weighing someone may not accurately determine if they are overweight. For example, two people may weigh 70 kg but one may be of an average weight whereas the other person is obese. Height is an important factor in determining if the person's weight is healthy for them. To take this into account, the relationship between weight and height is determined by calculating the body mass index (BMI).

A BMI of between 20 and 24.9 kg/m2 is desirable. A BMI of 25 kg/m2 or higher is overweight, and over 30 kg/m2 is classed as obese.

The distribution of fat on the body is also significant; carrying fat around the abdomen is associated with highest risk. This is termed ‘central obesity’ and people with this distribution are described as ‘apple-shaped’. A simple assessment for central obesity is to measure waist (or girth) circumference in centimetres using a tape measure (Figure 12c). Ideally, waist circumference in men should be less than 94 centimetres (cm), and less than 80 cm in women. (You may see other values quoted in other sources as the exact value is open to debate.) If these values are exceeded it is an indication of excessive body fat around the abdomen. A further calculation that can be made is the waist to hip ratio. The waist should be measured at the level of the umbilicus (belly button) and the hips at the widest point. The waist measurement is divided by the hip measurement. Ideally the ratio should be 1.0 or less in men or 0.8 or less in women.

Figure 12: Determining risk by calculating BMI and measuring the waist circumference.

Exercise 8

Mrs Soames has a BMI of 29 kg/m2 with a waist measurement of 92 cm. Her husband also has a BMI of 29 kg/m2 with a waist measurement of 92 cm. Who has the higher risk of coronary heart disease?


Mrs Soames has the higher risk. Although both of them are overweight, Mrs Soames has central obesity, with a waist measurement higher than is ideal for a woman.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371