Understanding BMI

The body mass index, or BMI, is commonly regarded as a good gauge of whether someone is a healthy weight. Why do you feel it’s a good measure of risk?

A high BMI can massively increase your risk of all sorts of conditions, not only things commonly known to be directly related to obesity like heart disease and diabetes but also things like joint issues and arthritis. Having a BMI and requiring surgery carries an increased risk. I was surprised to read that obesity and being overweight contribute to at least one in every 13 deaths in Europe. A high BMI might not only increase your risk of dying or having a critical illness but of being off work, so for all types of cover we need to assess BMI. It can also be linked with mental health issues. Often, we see depression going hand in hand with higher BMIs. As well as being overweight being underweight can be an issue.

What questions do you ask about BMI?

We ask on the application what is your height and what is your weight and from that we can calculate where someone sits on the body mass index. It is not an exact science. We tend to find that weight is one of the most common things that people under-disclose and they tend to over-estimate their height. Generally speaking, a BMI of less than 18.5 is regarded as underweight, 18.5 to 24.9 is regarded as normal, 25 to 29.9 as overweight, 30 to 34.9 as obese and above 35 as extremely obese. It can be important to view BMI in relation to age. Someone who is very overweight at a young age can be at greater risk. And especially as people get older, a low BMI – say 18 or lower – can put people at increased risk of frailty, falls, fractures and osteoporosis.

Is BMI the only metric you use or do you also consider body shape?

That is a tricky one. At the moment, we use BMI, which remains the most widely accepted way of evaluating the risk. Waist measurement is something we don’t currently ask at the moment or use as a factor when making a decision, but it may be something we consider for the future.

Using the waist-to-height ratio, in conjunction with BMI, can help to provide a practical estimate of central adiposity, which is the accumulation of fat around the abdomen, to help to assess and predict health risks, such as type 2 diabetes, hypertension or cardiovascular disease. A waist measurement of more than half of a person's height, is an indication of greater risk even if they have a normal BMI. So using waist measurement would mean that some customers would have to be charged a rating, or a higher rating, whilst a small proportion of customer may be able to have a rating reduced or be acceptable at Standard. At Zurich we did a comparison a few years ago using results from Nurse Screenings to see what impact using waist measurement would have and found that although a proportion of customers currently rated for BMI would see their ratings reduced, a similar proportion of customers would go from being accepted Standard to being rated.

We have also looked at a few studies and one by the British Heart Foundation found that on average, women under-estimate their dress size by one or two sizes and men their waist size by at least two inches, so it’s difficult to get an accurate measurement of a customer’s waist and know the best way of doing it. On the whole, BMI still seems to be the best way for the vast majority of customers and it’s the most widely recorded measurement in GP records. We seldom see waist measurements, though this is something that doctors are starting to record more. It may be that further down the line we are able to use the waist measurement as well as the height and weight to get a more complete picture. We don’t yet ask about exercise but this may also be something to consider for the future.

What are the possible outcomes of a very high or low BMI for applicants?

Typically, a BMI of 30 and above could entail a loading starting at 25% of the standard premium. From a BMI in the mid-30s you would be looking at a loading of 50-75%. The maximum loading for BMI alone would be 125-150%. Thereafter, we tend to decline those with a BMI or 40 or 41 looking for life insurance or slightly lower for critical illness cover and income protection. For customers with high BMIs over 38 to 40 (depending on age), their application will be referred to an underwriter to determine whether we can offer critical illness or not before determining whether we may need a Nurse Screening Exam to check the customer’s current BMI.

For more information on BMI and underwriting, you can download our BMI underwriting guide here.