March 09, 2016

Stature/body mass index and socioeconomic status

BMJ 2016; 352 doi: http://dx.doi.org/10.1136/bmj.i582 (Published 08 March 2016)

Height, body mass index, and socioeconomic status: mendelian randomisation study in UK Biobank 

Jessica Tyrrell, research fellow1 2, Samuel E Jones, associate research fellow1, Robin Beaumont, associate research fellow1, Christina M Astley, research fellow3 4, Rebecca Lovell, research fellow2, Hanieh Yaghootkar, research fellow1, Marcus Tuke, associate research fellow1, Katherine S Ruth, associate research fellow1, Rachel M Freathy, senior research fellow1, Joel N Hirschhorn, professor2 3 5, Andrew R Wood, research fellow1, Anna Murray, senior lecturer1, Michael N Weedon, associate professor1, Timothy M Frayling, professor1

Abstract

Objective To determine whether height and body mass index (BMI) have a causal role in five measures of socioeconomic status.

Design Mendelian randomisation study to test for causal effects of differences in stature and BMI on five measures of socioeconomic status. Mendelian randomisation exploits the fact that genotypes are randomly assigned at conception and thus not confounded by non-genetic factors.

Setting UK Biobank.

Participants 119 669 men and women of British ancestry, aged between 37 and 73 years.

Main outcome measures Age completed full time education, degree level education, job class, annual household income, and Townsend deprivation index.

Results In the UK Biobank study, shorter stature and higher BMI were observationally associated with several measures of lower socioeconomic status. The associations between shorter stature and lower socioeconomic status tended to be stronger in men, and the associations between higher BMI and lower socioeconomic status tended to be stronger in women. For example, a 1 standard deviation (SD) higher BMI was associated with a £210 (€276; $300; 95% confidence interval £84 to £420; P=6×10−3) lower annual household income in men and a £1890 (£1680 to £2100; P=6×10−15) lower annual household income in women. Genetic analysis provided evidence that these associations were partly causal. A genetically determined 1 SD (6.3 cm) taller stature caused a 0.06 (0.02 to 0.09) year older age of completing full time education (P=0.01), a 1.12 (1.07 to 1.18) times higher odds of working in a skilled profession (P=6×10−7), and a £1130 (£680 to £1580) higher annual household income (P=4×10−8). Associations were stronger in men. A genetically determined 1 SD higher BMI (4.6 kg/m2) caused a £2940 (£1680 to £4200; P=1×10−5) lower annual household income and a 0.10 (0.04 to 0.16) SD (P=0.001) higher level of deprivation in women only.

Conclusions These data support evidence that height and BMI play an important partial role in determining several aspects of a person’s socioeconomic status, especially women’s BMI for income and deprivation and men’s height for education, income, and job class. These findings have important social and health implications, supporting evidence that overweight people, especially women, are at a disadvantage and that taller people, especially men, are at an advantage.

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5 comments:

Krefter said...

Makes perfect sense. As much as in the modern world brains matter, people(employers, consumers, etc) still care a lot about looks(mostly in women) and strength(mostly in men).

Kostas said...

"overweight people, especially women, are at a disadvantage and that taller people, especially men, are at an advantage"

Interesting phrasing. I wonder why the chose it over something like: "overweight people, especially women, are at a disadvantage just like shorter people are, especially men."

What many people are going to take away from this is that men are at an advantage compared to women because of their height.

Are there any more details concerning the two effects on the two sexes?

A Res said...

I remember reading about a 19th century study that found the height of UK criminals was much shorter than the average, which may or may not have been the result of the effect of poor nutrition.
As for socio economic status that's often linked to IQ and education of course. I would guess anyone who would willingly eat something like fried mars bars might have a BMI problem and is probably not that far on the right hand side of the IQ curve to begin with.

nankoweap said...

Maybe their (implied) conclusion is backwards. Maybe other attributes that contribute to higher socioeconomic status are associated with greater height and lower BMI.

Matt said...

BMI will tend to be higher at lower heights, so long as there is no strong covariation between body mass and height, simply because BMI = mass / height (so if mass stays the same, while height increases or decreases, BMI and height will negatively correlate).

That might weaken the BMI causal pathway, opposed to the height pathway. BMI's probably more meaningful if you look within a height class (a population of men / women with exactly the same height, which is doable with a large sample size). Do larger and more robust men and women, of the same height, tend to have worse outcomes?

There's also your question of linearity - is mass important or central obesity, as measured (slightly messily) by being above a certain high BMI threshold or by direct waist circumference/height measures (ideally adjusted for lean mass)? Would we actually find that small differences in the overweight-normal weight categories matter, or that stronger effects kick in at conditions of obesity (effectively curvilinear).

There was a recent paper on European heights which found that BMI and height showed a negative genetic correlation. Not so surprising if mass increasing variants didn't increase along with height, as we might expect genetic body mass to be constrained to about the same level between different European populations who received similar levels of nutrition, over the long average. The genetic BMI-height scaling worked out to Europeans all having about the same "genetic body mass".