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05-07-2016 | Diabetes | News | Article

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Obesogenic environment magnifies genetic effect on BMI

medwireNews: The effect of genetic variants known to influence body mass index (BMI) has been increasing over more recent years, shows a study in JAMA.

Furthermore, the associations were stronger in Black than White participants, report Maria Glymour (University of California, San Francisco, USA) and co-researchers. They suggest this may reflect the general social disadvantage of Black people in the USA, noting also that they are more likely than White people to live in neighbourhoods with limited access to green space and fresh food.

The study relied on a US birth cohort that included 7482 people born between 1900 and 1958, and the team notes that participants born more recently were exposed to obesogenic environmental factors “at earlier developmental stages and for a greater fraction of their lives” than people born earlier.

Participants’ genetic risk for BMI was based on the weighted effects of 29 single nucleotide polymorphisms associated with BMI. In the cohort overall, each unit increase in the resulting genetic risk score (GRS-BMI) was associated with a 0.99-unit increase in BMI among White people and a 1.77-unit increase among Black people, much of which was accounted for by the FTO gene.

But the associations changed with year of birth. Among White people, after accounting for age, each unit increase in GRS-BMI was associated with a 1.37-unit BMI increase among those born after 1943, but just a 0.17-unit increase among those born before 1924.

Among Black people, the corresponding BMI increases were 3.70 units for those born after 1943 and 0.34 units for those born between 1924 and 1933, but 1.44 units for those born before 1924, although this was based on only 100 individuals, compared with 765 White people born in this era.

“The key implication is that genetic associations, even for physiologic measures such as BMI, are contingent on environmental context”, say Glymour et al.

However, they stress that their findings “leave open the critical question of which aspects of the environment interact with genetic risks.”

Overall, genetic risk accounted for just 0.99% and 1.37% of the variation in BMI among White and Black participants, respectively, and BMI rose in more recent years even among people with low GRS-BMI values.

“This underlines the limited importance of genetic risk factors in driving the obesity epidemic”, says the team.

By Eleanor McDermid

medwireNews is an independent medical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2016