Intended for healthcare professionals

Rapid response to:

Research News

Waist measurement, not BMI, is stronger predictor of death risk, study finds

BMJ 2017; 357 doi: https://doi.org/10.1136/bmj.j2033 (Published 26 April 2017) Cite this as: BMJ 2017;357:j2033

Rapid Response:

Normal weight central obesity: the value of waist-to-height ratio in its identification

The problems with normal weight central obesity

This article [1] quite rightly focuses on the problem of normal weight central obesity, which has received increased attention recently. Central obesity has several anthropometric proxies: waist circumference; waist-to-hip ratio and waist-to-height ratio (WHtR)are the commonest. People with normal weight central obesity show increased morbidity in relation to cardiometabolic risk greater than those in normal weight people without central obesity e.g. [2-4]. Further, their mortality is also increased e.g. [5-9].

NICE guidance

The National Institute for Health and Clinical Excellence (NICE) have just (April 24th 2017) re-issued their unchanged 2014 public health guideline on Weight management: lifestyle services for overweight or obese adults [10]. In this guidance, NICE acknowledge the importance of central obesity by stating that waist circumference can also be used to assess whether someone is at risk of health problems because they are overweight or obese (up to a Body Mass Index (BMI) of 35kg/m2).

In their document Obesity: identification, assessment and management [11], NICE expanded on this guidance and produced a BMI/waist circumference matrix. Increased risk was, however, only indicated if waist circumference was high in the overweight or obese 1 groups ( i.e. BMI 25 to 34.9) . Thus their advice would only pick up those who are overweight or obese AND have high waist circumference, not those with normal weight central obesity.

Whereas it is good to see that NICE now recognise the importance of central obesity, it is a shame NICE did not use the 2017 update of their 2014 guidance to highlight the problems of normal weight central obesity.

How big is the problem of normal weight central obesity in UK?

Using data from the last 2 years of the UK National Diet and Nutrition Survey (NDNS 2013-2014) (n= 1108 adults aged 19 and over), we have cross-classified respondents on the anthropometric indices BMI and waist-to-height ratio (WHtR). Approximately 25% of normal weight adults (just under 10% of all adults) would be classed as having normal weight central obesity i.e. BMI below 25 and WHtR above 0.5.

WHtR <=0.5 WHtR>0.5
Row N % Row N %
Adults BMI Under 18.5 100.0% 0.0%
18.5 and below 25 75.2% 24.8%
25 and below 30 15.9% 84.1%
30 and below 40 0.2% 99.8%
Over 40 0.0% 100.0%
Total 37.2% 62.8%

How do boundary values of BMI and WHtR classify the UK survey population ?

If we want to avoid ‘missing’ the normal weight central obese population, we suggest that waist-to-height ratio values are used to categorise any population . Using the NDNS adult sample described above, we found that WHtR >0.5 would put 63% at first level risk and WHtR >0.6 would put 22% of the adult population ‘at risk’. This compares with 59% who are above BMI 25 and 23% who are above BMI 30. Thus the size of the ‘at risk’ population would not vary greatly -but the normal weight central obesity population would not be ‘missed’ and those targeted would be more likely to have abnormal cardiometabolic risk factors [3].

Discussion

If we want a proxy for central obesity that will work in a public health context, it needs to be simple. We have advocated previously for first level risk to be denoted by waist-to-height ratio of 0.5 [12] and this value is now being used quite widely in surveys and studies e.g. [13, 14]. The size of the ‘at risk’ population has resource implications for public health purposes. For this reason, we now suggest that the second level of risk should be denoted by WHtR of 0.6 .

A boundary value of WHtR 0.5 to indicate the first level of risk translates into a simple public health message of "Keep your waist to less than half your height" [14, 15]. For obesity and diabetes, prevention should start in childhood and any early screening method should be simple and cheap. Ideally it should involve measurements which can be done reliably by parents or carers and WHtR has been shown to be suitable[16].

Measuring WHtR does not require weighing scales but would normally require a tape measure for height and waist circumference. However, to check if WHtR is more than 0.5 does not even need a tape. A piece of string will suffice [17]. The string is used to measure the person/child’s height and then it is folded in half to see whether it fits easily around the person/child’s waist. If it does not, early health risk is indicated and further care and screening should be done. This is already Government policy in Thailand [18].

Conclusion

We therefore strongly urge NICE to consider the problem of normal weight central obesity, and, at the same time to consider the use of waist-to-height ratio as a primary screening tool for identification of early health risk. Maybe they will do this in the next update of their clinical guidance [11]?

References

1. Wise J: Waist measurement, not BMI, is stronger predictor of death risk, study finds. British Medical Journal 2017, 357:j2033.
2. Srinivasan SR, Wang R, Chen W, Wei CY, Xu J, Berenson GS: Utility of waist-to-height ratio in detecting central obesity and related adverse cardiovascular risk profile among normal weight younger adults (from the Bogalusa Heart Study). Am J Cardiol 2009, 104(5):721-724.
3. Ashwell M, Gibson S: Waist-to-height ratio as an indicator of 'early health risk': simpler and more predictive than using a 'matrix' based on BMI and waist circumference. BMJ Open 2016, 6(3):e010159.
4. Thaikruea L, Thammasarot J: Prevalence of normal weight central obesity among Thai healthcare providers and their association with CVD risk: a cross-sectional study. Sci Rep 2016, 6:37100.
5. Coutinho T, Goel K, Correa de Sa D, Carter RE, Hodge DO, Kragelund C, Kanaya AM, Zeller M, Park JS, Kober L et al: Combining body mass index with measures of central obesity in the assessment of mortality in subjects with coronary disease: role of "normal weight central obesity". J Am Coll Cardiol 2013, 61(5):553-560.
6. Ashwell M, Mayhew L, Richardson J, Rickayzen B: Waist-to-height ratio is more predictive of years of life lost than body mass index. PLOS One 2014, 9 (9):e103483.
7. Sahakyan KR, Somers VK, Rodriguez-Escudero JP, Hodge DO, Carter RE, Sochor O, Coutinho T, Jensen MD, Roger VL, Singh P et al: Normal-Weight Central Obesity: Implications for Total and Cardiovascular Mortality. Ann Intern Med 2015.
8. Sharma S, Batsis JA, Coutinho T, Somers VK, Hodge DO, Carter RE, Sochor O, Kragelund C, Kanaya AM, Zeller M et al: Normal-Weight Central Obesity and Mortality Risk in Older Adults With Coronary Artery Disease. Mayo Clin Proc 2016, 91(3):343-351.
9. Hamer M, O'Donovan G, Stensel D, Stamatakis E: Normal-Weight Central Obesity and Risk for Mortality. Ann Intern Med 2017:1-2.
10. National Institute for Health and Clinical Excellence: Public Health Guidline 53: Weight management: lifestyle services for overweight or obese adults. 2014.
11. National Institute for Health and Clinical Excellence: Clinical guideline 189, Obesity: identifification, assessment and management. 2014.
12. Ashwell M, Gibson S: A proposal for a primary screening tool: 'Keep your waist circumference to less than half your height'. BMC medicine 2014, 12:207.
13. Hardy LL, Mihrshahi S, Gale J, Drayton BA, Bauman A, Mitchell J: 30-year trends in overweight, obesity and waist-to-height ratio by socioeconomic status in Australian children, 1985 to 2015. Int J Obes (Lond) 2017, 41(1):76-82.
14. Kazlauskaite R, Avery-Mamer EF, Li H, Chataut CP, Janssen I, Powell LH, Kravitz HM: Race/ethnic comparisons of waist-to-height ratio for cardiometabolic screening: The study of women's health across the nation. Am J Hum Biol 2017, 29(1).
15. McCarthy HD, Ashwell M: A study of central fatness using waist-to-height ratios in UK children and adolescents over two decades supports the simple message--'keep your waist circumference to less than half your height'. Int J Obes (Lond) 2006, 30(6):988-992.
16. Lim LL, Seubsman SA, Sleigh A, Bain C: Validity of self-reported abdominal obesity in Thai adults: a comparison of waist circumference, waist-to-hip ratio and waist-to-stature ratio. Nutr Metab Cardiovasc Dis 2012, 22(1):42-49.
17. Wise J: Piece of string can assess cardiovascular risk, study finds. British Medical Journal 2015, 350:h2434
18. Thaikruea L, Yavichai S: Proposed Waist Circumference Measurement for Waist-to-Height Ratio as a Cardiovascular Disease Risk Indicator: Self-Assessment Feasibility. Jacobs Journal of Obesity 2015, 1(2):1-7.

Competing interests: No competing interests

03 May 2017
Margaret A. Ashwell
Registered Nutritionist
Sigrid Gibson
Ashwell Associates and Cass Business School, London
Ashwell St, Ashwell, SG7 5PZ