Women who work night shifts do not face a higher risk of breast cancer, according to a major scientific analysis.
For decades, it has been suggested that burning the midnight oil could raise the risk of the killer disease.
But researchers have now quashed the fears, after finding no evidence of any greater odds of breast cancer in female night shift workers.
Charities have said the findings should ‘reassure the hundreds of thousands of women’ who work overnight.
For decades, it has been suggested that burning the midnight oil could raise the risk of the killer disease. But researchers have now quashed the fears
The study comes on the heels of a review by the International Agency for Research on Cancer on the link between shift work and cancer.
The body, part of the World Health Organization, concluded in 2007 that shift work which disrupts the sleep cycle was ‘probably carcinogenic’.
A possible link between exposure to electric light at night and an increased risk of breast cancer was first proposed more than 30 years ago.
It was feared shift work may disrupt the body’s internal clock, suppressing levels of the sleep hormone melatonin and raising oestrogen levels.
However, the evidence has been inconclusive and recent research has suggested there may be no impact on breast cancer risk after all.
Scientists at The Institute of Cancer Research, London, tracked more than 100,000 women over the course of a decade.
The study, considered to be the biggest of its kind, found one in 50 of the women went on to develop breast cancer.
However, it found no evidence that women who regularly worked night shifts face a greater risk of getting the killer disease.
The link remained true, regardless of the different types of work they did involving night shifts, and the age at which they started such work.
Volunteers were initially asked about their working habits over the last 10 years, including how often they done night shifts.
Almost a fifth of the women – around 17.5 per cent – reported having worked night shifts at some point during the study.
Data was also gathered on known risk factors, including obesity, physical activity levels, alcohol consumption and use of HRT.
The researchers, led by Dr Michael Jones and Professor Anthony Swerdlow, asked the participants the same questions six years later.
Baroness Delyth Morgan, chief executive of Breast Cancer Care and Breast Cancer Now, welcomed the results.
She said: ‘We hope these findings will help reassure the hundreds of thousands of women working night shifts.
‘This question has been widely debated in recent decades and has understandably caused concern.
‘And it’s encouraging that the evidence now suggests night shift work has no impact on breast cancer risk.’
Baroness Morgan added she now awaits the IARC’s review of the global evidence to ‘gain even more clarity on the issue’.
Dr Jones said he was pleased ‘to see more evidence suggesting night shifts are not linked with a higher risk of breast cancer’.
But he added the effects of a person’s body clock being disturbed ‘for very long periods of time’ remains a mystery.
The results of the study were published in the British Journal of Cancer.
Breast cancer is the UK’s most common cancer, with around 55,000 women and 350 men being diagnosed each year.
Maintaining a healthy weight, keeping physically active and drinking less alcohol can all lower the risk of the disease.
WHAT IS BREAST CANCER, HOW MANY PEOPLE DOES IT STRIKE AND WHAT ARE THE SYMPTOMS?
Breast cancer is one of the most common cancers in the world. Each year in the UK there are more than 55,000 new cases, and the disease claims the lives of 11,500 women. In the US, it strikes 266,000 each year and kills 40,000. But what causes it and how can it be treated?
What is breast cancer?
Breast cancer develops from a cancerous cell which develops in the lining of a duct or lobule in one of the breasts.
When the breast cancer has spread into surrounding breast tissue it is called an ‘invasive’ breast cancer. Some people are diagnosed with ‘carcinoma in situ’, where no cancer cells have grown beyond the duct or lobule.
Most cases develop in women over the age of 50 but younger women are sometimes affected. Breast cancer can develop in men though this is rare.
The cancerous cells are graded from stage one, which means a slow growth, up to stage four, which is the most aggressive.
What causes breast cancer?
A cancerous tumour starts from one abnormal cell. The exact reason why a cell becomes cancerous is unclear. It is thought that something damages or alters certain genes in the cell. This makes the cell abnormal and multiply ‘out of control’.
Although breast cancer can develop for no apparent reason, there are some risk factors that can increase the chance of developing breast cancer, such as genetics.
What are the symptoms of breast cancer?
The usual first symptom is a painless lump in the breast, although most breast lumps are not cancerous and are fluid filled cysts, which are benign.
The first place that breast cancer usually spreads to is the lymph nodes in the armpit. If this occurs you will develop a swelling or lump in an armpit.
How is breast cancer diagnosed?
- Initial assessment: A doctor examines the breasts and armpits. They may do tests such as a mammography, a special x-ray of the breast tissue which can indicate the possibility of tumours.
- Biopsy: A biopsy is when a small sample of tissue is removed from a part of the body. The sample is then examined under the microscope to look for abnormal cells. The sample can confirm or rule out cancer.
If you are confirmed to have breast cancer, further tests may be needed to assess if it has spread. For example, blood tests, an ultrasound scan of the liver or a chest x-ray.
How is breast cancer treated?
Treatment options which may be considered include surgery, chemotherapy, radiotherapy and hormone treatment. Often a combination of two or more of these treatments are used.
- Surgery: Breast-conserving surgery or the removal of the affected breast depending on the size of the tumour.
- Radiotherapy: A treatment which uses high energy beams of radiation focussed on cancerous tissue. This kills cancer cells, or stops cancer cells from multiplying. It is mainly used in addition to surgery.
- Chemotherapy: A treatment of cancer by using anti-cancer drugs which kill cancer cells, or stop them from multiplying
- Hormone treatments: Some types of breast cancer are affected by the ‘female’ hormone oestrogen, which can stimulate the cancer cells to divide and multiply. Treatments which reduce the level of these hormones, or prevent them from working, are commonly used in people with breast cancer.
How successful is treatment?
The outlook is best in those who are diagnosed when the cancer is still small, and has not spread. Surgical removal of a tumour in an early stage may then give a good chance of cure.
The routine mammography offered to women between the ages of 50 and 70 mean more breast cancers are being diagnosed and treated at an early stage.
For more information visit breastcancercare.org.uk or www.cancerhelp.org.uk
