Women at average risk of breast cancer in their 40s don't benefit from mammograms and should wait until age 50 to get them, say new guidelines released by the U.S. Preventive Services Task Force.

The recommendations put forth by the government-backed doctors' group are published Monday in the Annals of Internal Medicine. They go against the recommendations of the American Cancer Society, which suggests women get annual mammograms beginning at age 40.

The group commissioned two studies to look at the effectiveness of mammography, clinical breast examinations, breast self-examinations, digital mammography and MRIs in detecting breast cancer.

The studies found that mammograms in women aged 40 to 49 led to false positive tests that created a need for invasive procedures like biopsies and generated anxiety.

"The UTSF recommends against routine screening mammography in women aged 40 to 49 years," reads the report. Instead, women aged 50 to 74 are advised to get mammograms every two years. After age 74, there is a lack of evidence as to the effectiveness of mammography.

The task force also recommends women not be taught to perform breast self-exams.

Canada similar in its stance

The UTSF's recommendations are in line with Canada's position on mammograms. "Research has shown that regular screening mammograms are very effective at detecting breast cancer for women aged 50 to 69," reads the Canadian Cancer Society's website. "Accordingly, all provincially organized screening programs in Canada encourage women aged 50 to 69 to have regular screening mammograms."

Heather Chappell, director, cancer control at the Canadian Cancer Society in Toronto, told CBC News Tuesday that the screening guidelines apply to the population at large, and to women with no symptoms. She says women who have any symptoms or known risk factors should talk to their doctors about screening options, which may include mammograms, ultrasound or MRI.

"It needs to be an individual decision," she said, adding that women in their 40s need to arm themselves with information about their risk profile and to make an informed decision along with their physician about their need for earlier screening. Women with a history of breast cancer in their family, or those with the BRCA1 or BRCA II mutations are at higher risk of developing the disease.

The Canadian Cancer Society also recommends all women over the age of 40 have a clinical breast exam (performed by a doctor) every two years to screen for breast cancer.

Chappell says that the Canadian Cancer Society has moved away from advising women to conduct "prescriptive" regimented breast exams each month. Instead, it recommends women be body aware, checking for any changes in breast size, shape or feel.

Like the Canadian Cancer Society, the Canadian Breast Cancer Foundation also promotes breast health awareness.