Being underweight INCREASES the risk of breast cancer in pre-menopausal women, study finds

Being underweight increases the risk of breast cancer in pre-menopausal women, new research suggests.

Carrying too little weight between the ages of 18 and 24 is particularly risky, a UK study found today.  

Although the study’s authors did not speculate on why the findings occur, previous research suggests obesity leads to higher oestrogen levels, which can fuel breast cancer in postmenopausal women.

In pre-menopausal women, however, high oestrogen may protect against the disease due to them having healthier breast cells to start off with. Breast-cancer risk also increases with age. 

The researchers stress pre-menopausal women should not deliberately gain weight to reduce their breast-cancer risk.

Obesity is linked to many health problems, including heart disease, stroke, type 2 diabetes and kidney disorders. It is also the biggest cause of cancer after smoking.

Being underweight increases the risk of breast cancer in pre-menopausal women (stock)


Drinking just one small glass of wine a day raises a woman’s risk of breast cancer, a major report concluded in May 2017.

It means even following safe drinking guidelines of 14 units a week could be enough to endanger health.

A review of 119 studies, involving 12million women, found a daily glass of wine raises the risk of pre-menopausal breast cancer by 5 per cent and post-menopausal breast cancer by 9 per cent.

The authors, from the World Cancer Research Fund, estimated 12,000 cases of breast cancer could be prevented in the UK each year if nobody drank alcohol.

They based their calculations on consumption of 10g of alcohol a day, the amount in 100ml of 12 per cent strength wine – less than a standard 125ml small glass.

That is equivalent to 8.75 units a week, which is well within the 14 a week limit advised by the Government. 

How the research was carried out  

The researchers, from the Institute of Cancer Research, London, analysed 19 studies that investigated the link between BMI and the risk of breast cancer in a total of 758,592 pre-menopausal women.

The women had their BMIs measured at the ages 18-to-24, 25-to-34, 35-to-44 and 45-to-54. 

Of these, 13,082 developed the breast cancer over around nine years.

The findings were published in the journal JAMA Oncology. 

‘Gaining weight is not the answer’ 

Speaking of the findings, Rachel Rawson, senior clinical nurse specialist at Breast Cancer Care, said: ‘While these findings reveal an interesting dimension to what we know about obesity and breast cancer risk, maintaining a healthy weight remains one of the most important things you can do for your health.

‘Women call our helpline every day looking for ways to reduce their risk of breast cancer but for younger women, gaining weight is not the answer. 

‘It’s also important to remember that breast cancer is not common among younger women.’

Less than seven per cent of breast cancer diagnoses take place in women under 40 in the UK and US.  

Carrying too little weight between the ages of 18 and 24 is particularly risky (stock)

Carrying too little weight between the ages of 18 and 24 is particularly risky (stock)

What is the link between obesity and cancer? 

Despite the study’s findings, previous research suggests being overweight can cause many types of cancer.

Carrying excess fat effects the way people’s hormones impact their bodies’ cells, which may cause them to multiply and lead to tumours.

Fat cells also lead to inflammation, which makes cells divide faster and can cause cancer in the long term. 

After the menopause, oestrogen made by fat cells can cause cells in the breast and womb to divide faster.  

The cancers most associated with obesity include those of the breast, bowel, womb, food pipe, pancreas, kidney, liver, ovaries and thyroid.

Evidence suggests obese people’s cancer risk reduces if they lose weight.