Education and health are closely associated though formal education's capacity to prevent HIV infection is still debated.
The study, published in The Lancet Global Health, suggests expanding secondary schooling could be a cost-effective strategy for preventing HIV infection.
"This study is among the first to provide causal evidence that secondary education is an important causal determinant of HIV infection," says senior author Prof. Jacob Bor of Boston University School of Public Health, MA. "Our results suggest that schooling should be considered alongside other proven interventions as part of a multi-pronged 'combination' HIV prevention strategy."
He explains that it is difficult to isolate the effect of education on the risk of HIV infection from the complex web of associated factors such as family background, socioeconomic status and psychological traits. This difficulty necessitates the use of "natural experiments" to provide evidence to guide healthcare policies.
In the absence of large-scale trial data, the researchers used a recent school policy reform in Botswana as the basis for their study in order to assess what role an increase in the number of years spent in secondary school played in the risk of HIV infection.
Botswana is one of the most HIV-affected countries in the world. In 2013, around 22% of adults aged 15-49 were estimated to be infected with the virus.
In 1996, free grade 10 education was provided as part of junior secondary school, resulting in an average increase of 0.8 years of schooling among teenagers in the country. Using data collected in 2004 and 2008 from the nationally representative Botswana AIDS Impact Surveys, the researchers were able to compare birth cohorts exposed to extended secondary education with those that were not.
The researchers analyzed data for 7,081 men and women who were aged 18 and above at the times the surveys were conducted. Any who were born in or after 1981 were classified as having been exposed to the secondary school policy reform.
Effect of extended schooling on HIV risk more apparent among women
From the data, they estimate that those who received an extra year of secondary schooling were 8 percentage points less likely to test positive for HIV infection a decade later, with around 17% of the cohort infected compared with 25% of those who did not receive an extra year.
The effect of extra secondary schooling appeared to be more pronounced among women, whose risk was reduced by 12 percentage points with an additional year of secondary schooling.
Co-author Jan-Walter de Neve, a doctoral student at Harvard T.H. Chan School of Public Health in Boston, MA, states that secondary schooling may be particularly effective in reducing HIV risk by targeting a critical period of growth in adolescence:
"Information about prevention methods and reasoning skills gained in school may play a preventative role against HIV, enabling people with education to adopt healthy strategies to avoid infection. Additionally, education may expand economic opportunities and reduce women's participation in higher risk transactional sexual relationships."
"Expanding the opportunities of young people through secondary schooling will not only have economic benefits but will also yield health benefits and should be a key priority for countries with generalized HIV epidemics," Prof. Bor adds.
In a linked Comment, Dr. Karen Ann Grépin from Robert F Wagner's Graduate School of Public Service, New York University, NY, notes that the fact the results were strongest among women was especially important considering the worldwide inequities in access to secondary schooling for girls.
"[Increasing] access to education in low-income countries should be an important priority because of the proven economic returns to such investments," she concludes. "The health returns from education, such as its potential role in HIV and child mortality should also make it a top priority for the global health community."
A recent report from the UNAIDS and Lancet Commission states that efforts to prevent new HIV infections must accelerate over the next 5 years, otherwise deaths from AIDS will increase worldwide.