Living on a brightly-lit street could raise your breast cancer risk by 14%

STREET lights may increase the risk of breast cancer, research suggests.

Experts found that women who lived in areas lit up more brightly at night were more likely to develop the disease.

The researchers from Harvard Medical School suspect bright artificial lights disrupt the human body clock, which in turn disrupts hormone levels and raises the chance of breast cancer developing.

They tracked 110,000 participants across the US for 15 years, comparing breast cancer rates in different areas to satellite images taken at night. Women in areas that were in the brightest 20 per cent at night were 14 per cent more likely to get breast cancer than those in the darkest 20 per cent, according to results published in Environmental Health Perspectives journal.

Our body clock is regulated by the senses, most importantly the perception of light and dark. The mechanism rules our daily rhythms, including our sleep and waking patterns and metabolism.

But the pressures of modern living mean we are now increasingly working against our clocks and risking long term health problems from metabolic disease. Separate studies have found that people who work night shifts or who get too little sleep are more susceptible to conditions including depression, diabetes and obesity.

The researchers said the presence of bright light decreases the body’s production of melatonin, a hormone that anticipates the onset of darkness and dictates our sleep patterns. Levels change throughout the day, typically reaching a peak in the evening.

Women with less melatonin have been found to have a higher risk of breast cancer. In the lab, melatonin has been shown to slow tumour growth. Researcher Professor Peter James said: ‘In our modern industrialised society, artificial lighting is nearly ubiquitous. Our results suggest that this widespread exposure to outdoor lights during nighttime hours could represent a novel risk factor for breast cancer.’

The researchers said the link was found only among pre-menopausal women and those who had ever smoked. It was stronger among night shift workers.