Two new studies on popular drinks show mixed news for consumers.

One study presented at the 10th American Association for Cancer Research International Conference on Frontiers in Cancer Prevention Research in Boston showed that women who drank more than three cups daily of caffeinated coffee had a 20 per cent lower risk of getting the most common form of skin cancer.

Among male coffee drinkers, the risk of basal cell carcinoma was 9 per cent lower.

"Given the nearly 1 million new cases of BCC diagnosed each year in the United States, daily dietary factors with even small protective effects may have greater public health impact," The Australian quoted researcher Fengju Song, a postdoctoral fellow at the Department of Dermatology at Brigham and Women's Hospital in Boston and Harvard Medical School.

The study was based on data from the Nurses' Health Study at Brigham, which had about 73,000 participants, and the Health Professionals Follow-Up Study at Harvard, which had about 40,000 participants.

Coffee-drinking failed to provide protection against two other prevalent types of skin cancer - squamous cell carcinoma and melanoma. BCC often hits people with light hair, green or blue eyes and often manifests as a skin sore than bleeds and doesn't heal.

In the other study led by researchers from the University of Vermont, a link was found between regular consumption of fizzy soft drinks and aggression and violence in teenagers.

The researchers did not declare a causal link. The study, published in the Injury Prevention journal, had 1,878 teen respondents from 22 Boston schools with ages from 14 to 18.

Frequent non-diet soft drinks consumption based on an average of five cans per day was associated with a 9 to 15 per cent higher likelihood of engaging in violent behaviour toward a peer, sibling or partner or carrying a gun or knife.

The rate of violent behaviour went up as the teens drank more fizzy beverages.

"There may be a direct cause-and-effect relationship, perhaps due to the sugar or caffeine content of soft drinks, or there may be other factors, unaccounted for in our analyses, that cause both high soft drink consumption and aggression," wrote Dr. Sara Solnick from the University of Vermont.

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