NEW YORK (Reuters) -- Women choosing breast implants have 'at-risk' lifestyles which can contribute to disease, further clouding the ongoing controversy as to the health risks involved in breast augmentation, says a new study.

"Women who have breast implants for the purpose of augmentation may have... differences that potentially make these women more or less likely to develop certain diseases," according to a study led by researchers from Seattle's Fred Hutchinson Cancer Research Center. The study is published in the current issue of The Journal of the American Medical Association (JAMA).

Controversy over suspected links between silicone breast implants and diseases such as cancer, lupus, and arthritis have led to lawsuits and bans on certain forms of breast implants.

The researchers surveyed over 3,500 adult, white women residing in Washington state. Eighty of those women had undergone breast augmentation for nonmedical reasons, usually between the ages of 25 and 44.

The study authors compared the lifestyle factors of those 80 women to the rest of the study subjects. They found that compared with women without implants, women who had had breast augmentation:

-- were nearly three times as likely to drink more than seven alcoholic beverages a week.

-- were nine times as likely to have at least 14 sexual partners during their lifetime, twice as likely to have used oral contraceptives, 1.5 times as likely to have become pregnant by age 20, and twice as likely to have at least one terminated pregnancy.

-- were 4.5 times more likely to use hair dyes.

-- were less likely to be overweight.

Many of these factors are what the researchers call "confounders" for disease -- lifestyles or attributes common to a certain group of individuals which could influence their chances of contracting various illnesses.

These confounders could be important, experts say. For example, previous studies have suggested a link between breast implants and connective tissue diseases. However, according to the researchers, "some studies... suggest that the use of hair dyes... may increase the risk of systemic lupus erythematosus or systemic scleroderma."

The hair dye confounder may lessen fears that implants are behind the raised lupus/scleroderma risk in those women choosing breast augmentation. The authors reason that breast implants may be only part (or none) of the reason why this subset of women are more prone to those types of disease. But other confounding factors may actually "mask" an increased risk for disease, according to the study authors.

For example, they point out that women using the Pill seem to have a decreased overall risk for rheumatoid arthritis. Rheumatoid arthritis has also been linked to breast implants. But the protective effect of oral contraception, more frequently used by the 80 women with breast implants, "could mask an elevation in the risk of rheumatoid arthritis associated with having breast implants," the researchers say. In other words, that risk could be even higher than once assumed.

Since the breast-implant subjects were also more likely to be thinner than their unaltered peers, that same 'masking' of risk could be occurring in respects to weight-related diseases, such as heart disease and diabetes.

In a comment on the study, also published in the current issue of JAMA, Dr. Deborah del Junco of the Veterans Affairs Medical Center in Houston says that neglecting the influence of confounders like these often ends up in "either creating a false association or obscuring a true association" between one factor (breast implants) and disease risk (lupus, for example).

And del Junco believes this study should inspire scientists to dig deeper before issuing health warnings based on one factor alone. SOURCE: The Journal of the American Medical Association (1997;277(20):1612-1617, 1643- 1644)