Good health and a long life may have more to do with how you grew up than how much education you have under your belt, research from Denmark hints.
Studies, including the Danish one, have generally found that people with more education tend to live longer and are healthier than those with shorter transcripts.
But in the small Scandinavian country, much of that effect vanished when comparing twins who differed in how long they had been in school.
"We were interested in the social inequality in health that we see on the population level," said Mia Madsen, a doctoral candidate at the University of Southern Denmark, Odense, who worked on the study. "What's so great about the twins is that you can use them to get a little closer to understanding that inequality."
Madsen said her study was one of the largest of its kind so far. Tapping into national data from 1921 to 1950, she and her colleagues searched for same-sex or identical twins whose educations differed in length and at least one of whom had died.
The researchers found more than 2 000 twin pairs. Overall, the ones with no more than seven years of study - the minimal requirement - were about 25 percent more likely to have died. But when comparing twins within each pair, both for identical and same-sex twins, that difference became much less pronounced and could have been due to chance.
"The social inequality seems to get smaller when you account for genetics and upbringing," said Madsen. "Maybe it's an indication that very early life conditions play a big role later on."
She added that an earlier study, based on the same data, had found a similar pattern in the twins' general health, also stressing the importance of early life conditions. What those might be is still up in the air, but Madsen said unhealthy eating habits were one likely culprit.
Still, the researchers said the picture wasn't clearcut. When focusing on those twin pairs who had the largest difference in education - at least eight years - they did find a positive effect on life span.
Madsen said her findings seemed at odds with some of the research from the US.
Still some uncertainty
"When I look at the twin literature on social inequality, I see two different pictures in Denmark and the US," she said, noting that the two countries had different access to healthcare. "It makes sense that your social position and education in adulthood would matter more in the US than in Denmark."
Maria Glymour, of the Harvard School of Public Health in Boston, said twin studies were sometimes hard to interpret because twins with the right differences are hard to come by. Even with a study as big as this there is still a lot of uncertainty, she said.
"To the extent that there are differences between the results of this study and prior work in the US, it is likely due to study design differences, not necessarily differences in medical care," she said.
"Inequalities in health by education level have been shown in many countries with universal access to medical care, so these inequalities must partially be driven by other pathways."
However, Glymour said the idea that some of the tie between education and life span might be explained by early life conditions was important.
"It would help us understand the most important ways to focus resources for children." - (Reuters Health, June 2010)