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British scientists say they have uncovered a new risk factor that makes some women prone to developing breast cancer.

Women with one breast significantly larger than the other are more likely to get the disease, according to the research team at the University of Liverpool.

Their study is based on an analysis of mammograms taken almost three decades ago. The researchers compared the breast symmetry of 252 women who went on to develop breast cancer with 252 women who remained free of the disease. The findings revealed that the risk of getting cancer rose by 50 per cent for each 100-millilitre increase in breast asymmetry. (In other words, the volume of one breast was 100 ml greater than the other.)

"One hundred ml is quite a big difference," said lead researcher Dr. Diane Scutt, noting that women who took part in the study had an average breast volume of 500 ml.

Dr. Scutt said women shouldn't be overly alarmed if their breasts are not the same size. In fact, some degree of difference is normal. "Only 1 per cent of women in our sample had perfectly symmetrical breasts," she said in an e-mail interview. "Like any potential risk factor, it can't be taken in isolation but should be seen in light of a woman's entire risk profile," such as genetic history and the timing of the onset of menstruation and menopause.

"Some women had a lot of asymmetry and didn't get breast cancer, some had very little and did." The average asymmetry was approximately 60 ml.

The researchers are not sure why breast asymmetry seems to be linked to the development of cancer. But, in the journal Breast Cancer Research, they speculate that it may be more difficult for the body to develop breasts relatively equal in size if the tissue contains harmful mutations.

Mammograms safe

Women born with mutations in either the BRCA1 or BRCA2 genes face a daunting future: There is an 80-per-cent chance they will develop breast cancer -- and, more often than not, it strikes at an early age. So doctors urged them to go for regular mammograms (starting at the age of 25) to make sure that a tumour isn't growing in one of their breasts.

However, some researchers have questioned this practice, concerned that frequent mammograms could further heighten the risk of cancer. Mammograms expose the breast to a small amount of radiation. The dose in not considered high enough to raise the risk of breast cancer in the general population. But, this particular group of women might be more sensitive to the DNA-damaging effects of radiation, some researchers have speculated. In healthy people, the BRCA1 and BRCA2 genes play a role in the repair of DNA breaks. So women with mutations in these genes might be especially vulnerable to DNA breaks induced by ionizing radiation.

But a new study, led by Steven Narod at the Centre for Research in Women's Health in Toronto, has found that there is no need for these women to fear mammography. Using data involving 3,200 women from Canada, the United States, Europe and Israel, the team found no evidence that mammograms sped up the onset of cancer.

The study is being published in The Lancet Oncology.

Fumes fuels bad bacteria

Children who grow up in homes with smokers are more likely to be carriers of potentially harmful bacteria that could make them vulnerable to both minor and major infections.

Israeli researchers took nose and throat swabs of 200 children to determine if they carried Streptococcus pneumoniae. About 76 per cent of the kids exposed to tobacco smoke carried the bacteria, also known as pneumococci, compared with 60 per cent of those who lived free of fumes.

If the bacteria grow out of control, infection can result in minor illnesses such as ear infections or lead to more serious diseases like sinusitis, pneumonia or meningitis, said lead researcher Dr. David Greenberg at Ben-Gurion University of the Negev. And, he noted, a "higher carriage rate," is the first step to infection.

Dr. Greenberg isn't sure why the kids might be little bastions of nasty microbes. But in an e-mail interview he speculated that smoke may be "harmful for 'good bacteria,' which are part of the environment of the nose and throat." And any change in the normal equilibrium might tip the balance in favour of "bad" bacteria, allowing pneumococci to run wild. The study is being published in the journal Clinical Infectious Diseases.

Atkins's safety challenged

The once-popular Atkins diet seems increasingly less popular these days.

The high-protein, low-carbohydrate fad isn't safe and should not be used for losing weight, according to a dire warning in The

Lancet.

Doctors in New York City tell the tale of a 40-year-old obese woman who developed potentially life-threatening complications after strictly adhering to the diet for a month, eating only meat, cheese, salads and certain supplements. She checked into a local hospital, complaining of nausea and frequent vomiting.

The medical team, lead by Dr. Klaus-Dieter Lessnau, diagnosed her with ketoacidosis -- in which dangerously high levels of acids, called ketones, build up in the blood stream. (Ketones are produced by the breakdown of fat for energy.) Although the woman had other underlying medical problems, the doctors concluded that the Atkins diet had triggered her condition.

In a commentary published with the report, Lyn Steffen of the University of Minnesota states that "Low-carbohydrate diets for weight management are far from healthy, given their association with ketosis, constipation or diarrhea, halitosis, headache and general fatigue."