The relative impact of genetics on height doesn't increase with improvements to the standard of living.

These are among the findings of an international research group that analyzed the impact of genetic and environmental factors on adult height over a span of more than a century. The research inluded 40 twin cohorts, including more than 143,000 twin pairs from 20 countries.

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The published study shows no clear trend is apparent in the proportion of height variation explained by genetic differences between individuals, or heritability, between birth year cohorts from 1886 and 1994.

"Our results do not support the assumption that the heritability of height increases as the standard of living improves and extreme poverty is reduced," said researcher Aline Jelenkovic from the University of Helsinki.

When geographical-cultural regions were studied separately, height variation was lowest in East Asia and greatest in North America and Australia. The geographical differences in height variation can be attributed to both genetics and environment.

Hereditability estimates by geographical-cultural regions did not show a pattern across birth cohorts.

"Even though mean height has increased over the 20th century as standards of living have improved, this is not reflected in the heritability of height," said Jelenkovic.

Variation in adult height in human populations is caused by individual genetic differences and environmental factors.

Twin and family studies have consistently shown the proportion of height variation attributable to individual genetic differences is some 80%. There has been a long-term hypothesis that the impact of genetic factors is weaker in populations with low living standards can lead to a lack of basic necessities, which are important for human growth.

Environment, however, is more significant for women's height.

The study showed that height variation caused by genetic differences was generally more pronounced among men than women. Conversely, environmental factors had a bigger impact on the height variation among women.

"This is to say that women's growth is not more resistant to environmental influences than that of men," said Jelenkovic.

TagsGenetics, height, standard of living, Aline Jelenkovic, Hereditability, Environment