NEW YORK – Babies born to mothers with high levels of arsenic exposure are five times more likely to die before their first birthday than infants whose mothers had the least exposure to the toxic mineral, new research shows.
"We observed clear evidence of an association between arsenic exposure and infant mortality," Dr. Anisur Rahman of Uppsala University Hospital in Sweden and colleagues state in the November issue of Epidemiology. And the fact that death risk increased as exposure rose, they add, "is supportive of a causal relationship."
The study was conducted in Bangladesh, where millions of tube wells dug 30 years ago to improve the country's water supply are now known to be contaminated with naturally occurring arsenic.
Public health experts estimate that as many as 77 million people in Bangladesh have been poisoned by arsenic in drinking water; potential approaches to reducing exposure include filtering water through pond sand, using different types of wells, and harvesting rainwater.
Arsenic causes cancer, and has also been linked to diabetes, high blood pressure, and many other chronic illnesses. But studies investigating the effects of prenatal arsenic exposure have had mixed results, Rahman and colleagues say.
Many previous studies were retrospective, meaning researchers asked women about pregnancy outcomes after the fact and their responses are therefore less reliable, the researchers explain. Most studies have also measured the amount of arsenic found in local drinking water but have not looked at how much water women actually consumed during pregnancy, they note.
To address these issues, the researchers followed 2,924 pregnant women who provided urine samples for arsenic testing, all when they were eight weeks pregnant, and some later in pregnancy. About nine percent of the women miscarried, three percent had abortions, and two percent had stillborn babies.
Eighty-six percent of the women had live births, while about four percent of these babies died before they were 12 months old.
Women in the top fifth based on their arsenic exposure had urine concentrations that ranged from 249 to 1,253 micrograms per liter; those in the bottom fifth had concentrations below 33 micrograms per liter.
In the U.S., urine arsenic levels between zero and 35 micrograms per liter are considered normal.
The most heavily exposed women in the study were 40 percent more likely to miscarry than those with the lowest exposure; however, this relationship was relatively weak and could have been due to chance, the researchers say.
The investigators also didn't see a dose-response relationship, meaning the risk of miscarriage didn't rise steadily as exposure increased. Nor was a clear association between arsenic exposure and risk of stillbirth seen in the group.
But the researchers did find a strong dose-response relationship between arsenic exposure and infant mortality risk. Among the women who gave birth to a live baby, those in the top fifth for arsenic exposure were five times as likely to see their infant die before his or her first birthday compared with those in the bottom fifth.
The infants died of a range of causes, including infections and impaired growth, and the researchers say more study is needed to understand exactly how a mother's arsenic exposure may contribute to the baby's risk of a premature death.