A long-awaited study by the U.S. Centers for Disease Control and Prevention shows a link between tainted tap water at a U.S. Marine Corps base in North Carolina and increased risk of serious birth defects and childhood cancers.

The authors of the study on Camp Lejeune released late Thursday by the CDC's Agency for Toxic Substances & Disease Registry warned it is based on a small sample size and cannot prove exposure to the chemicals caused specific individuals to become ill.

But the study did conclude that babies born to mothers who drank Lejeune tap water while pregnant were four times more likely than women who lived off-base to have such serious birth defects as spina bifida. Babies whose mothers were exposed also had a slightly elevated risk of such childhood cancers as leukemia, according to the results.

The study surveyed the parents of 12,598 children born at Lejeune between 1968 and 1985, the year most contaminated drinking water wells were closed. They reported 106 cases of serious birth defects and childhood hematopoietic cancers. Of those, researchers said they could obtain medical records to confirm the diagnoses in only 52 cases.

Epidemiologist Richard W. Clapp, who serves on a federal board that has reviewed the Lejeune contamination, said the links found through the study might "appear to be weak" due to the relatively small sample size. But he said the findings are important because they show strong evidence the water that Marines and their families drank, cooked with and bathed in might have made some sick.

"The fact that there was anything found is pretty important," said Clapp, professor emeritus at Boston University's School of Public Health. "This is an insensitive tool that we use here, these epidemiological studies. So the fact that they found anything is sort of remarkable."

The study looked back through time and was designed to see if there was a link between exposure to certain chemicals and certain health problems that developed later. This type of study is often used to investigate disease outbreaks, when health officials are trying to identify possible reasons for the illnesses.

There are no records to measure how much tainted water those surveyed consumed. Therefore, the study had to use complex modeling to gauge how much of the chemicals they could have been exposed to. The study also did not look at the health effects on adults that drank the water. More than 80 men with Lejeune ties have been diagnosed with an extremely rare form of breast cancer.

In the nearly three decades since the contamination was first disclosed to the public, military officials have repeatedly issued public statements downplaying health risks from drinking the tainted water prior to the closure of the most contaminated wells.

A brief statement issued Thursday by Lejeune spokeswoman Capt. Maureen Krebs contained no such disclaimers. It stressed that the water currently flowing from the base's taps is routinely tested and safe to drink.

"These results provide additional information in support of ongoing efforts to provide comprehensive science-based answers to the health questions that have been raised," the statement said. "The Marine Corps continues to support these initiatives and we are working diligently to identify and notify individuals who, in the past, may have been exposed to the chemicals in drinking water."

Krebs said Friday she could provide no comment about the new report beyond the written statement.