Heavy drinking can lead to a number of serious health problems, including increased risk of cancer, heart disease, and dementia, but consuming even moderate levels of alcohol could be dangerous, as well, new research suggests.

The study, published in The BMJ, finds that moderate drinkers were three times more likely to experience a decline in mental skills than people who drank no alcohol at all.

For the study, researchers analyzed data on weekly alcohol intake in 550 healthy British men and women over a period of 30 years. The participants had an average age of 43 at the start of the study in 1985 and none were alcohol dependent.

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They were given brain function tests at regular intervals, and during the last three years of the study participants underwent an MRI brain scan.

The results showed heavy alcohol consumption over the 30-year period was associated with increased risk of hippocampal atrophy, a form of brain damage that affects memory and spatial navigation.

Heavy consumption was defined as more than 30 units of alcohol per week, with one unit of alcohol equivalent to 8 grams. "So a 175ml glass of wine [14% alcohol] has 2.4 units, and a pint of beer [5.2% alcohol] has 3 units," explains study author Anya Topiwala, a clinical lecturer in the department of psychiatry at the University of Oxford.

While previous research has suggested light-to-moderate drinking may have a protective effect on brain health, the new study showed the opposite, actually finding evidence of harmful associations.

While heavy drinkers were at the highest risk, those drinking moderately (14 to 21 units per week — about 5 to 7 beers or 6 to 8 glasses of wine) were three times more likely to have hippocampal atrophy compared with those who did not drink.

Furthermore, people drinking more than seven units of alcohol per week experienced a faster decline in language fluency over the study compared to those who abstained from alcohol.

The authors adjusted for several factors that could have influenced the results, including age, sex, education, social class, physical and social activity, smoking, stroke risk and medical history.

Topiwala said she was surprised by the findings. "As previous studies had reported the moderate drinking was protective against cognitive decline and dementia, we expected to find a similar association with adverse brain outcomes, which could underlie the protection," she told CBS News. "Instead we found the opposite."

While Topiwala acknowledges that more research is needed to confirm the findings, she said the study has important public health implications.

"I would suggest these findings raise a question mark over the safety of current U.S. alcohol guidelines, as we found evidence of associations with multiple harmful brain outcomes in individuals drinking within these limits," she said.

According to the U.S. Department of Health and Human Services and U.S. Department of Agriculture's dietary guidelines, moderate alcohol consumption is defined as having up to one drink per day for women and up to two drinks per day for men.

In an accompanying editorial, Killian Welch, consultant neuropsychiatrist at the Royal Edinburgh Hospital, says the findings "strengthen the argument that drinking habits many regard as normal have adverse consequences for health."

"This is important," he writes. "We all use rationalizations to justify persistence with behaviors not in our long term interest. With publication of this paper, justification of 'moderate' drinking on the grounds of brain health becomes a little harder."