Experts say that nearly half of women aged 40 and older who get mammograms are found to have dense breasts. Breast density is often inherited, but other factors can influence it. Factors associated with lower breast density include increasing age, having children, and using tamoxifen. Factors associated with higher breast density include using postmenopausal hormone replacement therapy and having a low body mass index.

Achille Manirakiza, an oncologist at King Faisal Hospital, says that breast density is normal and depends on a number of things, like age (younger age, premenopausal women tend to have denser tissues), phases of the menstrual cycles (less density is observed in the 1-2 weeks post-menstrual period).  

"There are other factors that are related also to body habitus (smaller breasts tend to correlate with higher density), the number of pregnancies (less correlate with density), and use of hormonal therapy,” he says.

Dr Manirakiza Wexplains that breast density can be a risk factor for cancer and might go undetected, as one of the best ways of breast cancer screening is a mammogram.

"As breast density is only a radiologic finding, not a physical examination finding, breast density might hide a malignancy or a mass on a mammogram.”

What are the causes?

According to Mayo Clinic, it’s not clear why some women have a lot of dense breast tissue and others do not. You may be more likely to have dense breasts if you:

• Are younger — Your breast tissue tends to become less dense as you age, though some women may have dense breast tissue at any age.

• Have a lower body mass index — Women with less body fat are more likely to have denser breast tissue compared with women who are obese.

•Take hormone therapy for menopause — Women who take combination hormone therapy to relieve signs and symptoms of menopause are more likely to have dense breasts.

When to see a doctor

According to Dr Manirakiza, breast density is an independent risk factor of breast cancer and the screening modes remain the same.

"A self-breast examination is strongly recommended as a way to detect early any changes in the breast characteristics. As density could change depending on the phase of the menstrual cycle, regular self-checking is key,” he advises.

An article on breast density by National Cancer Institute, states that only a mammogram can show if a woman has dense breasts. Dense breast tissue cannot be felt in a clinical breast exam or in a breast self-exam. For this reason, dense breasts are sometimes referred to as ‘mammographically dense breasts’.

How are dense breasts assessed?

According to doctors, mammography is used most commonly to determine whether a woman has dense breasts.

Healthline explains that radiologists who interpret mammograms subjectively determine the proportion of dense breast tissue (white on mammography) and non-dense fatty tissue (dark on mammography) using a visual scale and assign one of four levels of breast density:

•Almost entirely fatty breast: The breast is almost entirely composed of fatty tissue.

•Scattered areas of fibro glandular density: The majority of the breast is fatty tissue with some scattered areas of dense breast tissue.

•Heterogeneously dense: The majority of the breast is dense glandular and fibrous tissue with some areas of less dense fatty tissue.

• Extremely dense: The breast is almost all dense glandular and fibrous tissue.

The majority of women (8 out of 10) are classified in one of the two middle categories. Only a small fraction of women have either extremely dense breasts or breasts that are almost entirely fat.

 Dr Manirakiza says that there is no evidence of existing treatment for increased breast density. In case it is found, and the patient has a suggestive family history, a screening regimen is drawn, taking into consideration all the risks.