What's the Connection Between Bone Density and Breast Cancer?

Treatment for breast cancer can be a harsh affair. In attempting to save the life of the patient from the most imminent threat -- that posed by the cancer itself -- some treatments can cause painful or life-altering side effects. With some of these side effects, such as hair loss from chemotherapy, once the treatment has concluded, the side effect will disappear. Your hair nearly always grows back. But some other side effects can stick with you for the rest of your life.

Among these more long-lasting side effects is osteoporosis. The National Institute of Arthritis and Musculoskeletal and Skin Disease reports that "osteoporosis is a condition in which the bones become less dense and more likely to fracture." These fractures can cause pain and disability, and it's estimated that more than 53 million people in the United States already have or are at high risk for osteoporosis because of low bone mass. It's also known as a "silent disease because, if undetected, bone loss can progress for many years without symptoms until a fracture occurs," the NIAMSD reports.

Osteopenia (which is not a disease but refers to a thinning of the bones that can put you at increased risk of bone fractures) and osteoporosis are common conditions that affect many older women regardless of their breast cancer status. That's because estrogen levels change as we age. Estrogen has been found to have a protective effect on bone density, so as women's hormonal mix shifts after menopause, that can lead to a thinning of the bones. This in turn can lead to an increased risk of fractures, a probability that is more pronounced among Asian and Caucasian women, the NIAMSD reports.

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Some treatments for breast cancer can have the same effect, pushing women into early menopause and potentially impacting the strength of their bones. Dr. Robert Wesolowski, assistant professor of medicine at The Ohio State University Comprehensive Cancer Center -- Arthur G. James Cancer Hospital and Richard J. Solove Research Institute, says that treatment can lead to bone loss in some patients.

"Chemotherapy can change ovarian function from premenopausal to postmenopausal," he says, effectively pushing some women into early menopause. The older the premenopausal patient is when chemotherapy commences, "the more likely the chemo would ablate ovarian function and induce menopause," he says.

But it's not just chemo that poses a risk. Hormonal treatments for breast cancer can also lead to a thinning of the bones. "We increasingly use medication to artificially suppress ovarian function because we think by doing that, we reduce estrogen exposure and lower the risk of recurrence of breast cancer," Wesolowski explains. Among these treatments is a class of drugs called gonadotropin-releasing hormone agonists, or GnRH agonists for short. These drugs are delivered as an injection and they "shut down the ovaries in premenopausal women." These drugs are also used with in vitro fertilization, to suppress hormone levels for individuals undergoing sex reassignment and to treat other hormone-related disorders such as endometriosis and uterine fibroids. They're powerful drugs that shut off estrogen production in the ovaries but can cause menopausal-like side effects including insomnia, vaginal dryness, night sweats and bone loss.

Other endocrine therapies for breast cancer patients may also elevate your risk of developing osteoporosis or experiencing painful fractures. Aromatase inhibitors are a class of drugs used primarily in postmenopausal women to treat hormonally-driven breast cancers -- so-called ER- and PR-positive breast cancers that use hormones to grow. Aromatase inhibitors are more commonly used in postmenopausal women because the ovaries aren't the only estrogen production area. Adipose, or fatty, tissue and the adrenal glands also contribute to the production of estrogen in the body, and that process carries on after menopause. These medications inhibit estrogen production in adipose tissue and also suppress conversion of adrenal hormones into estrogen.

Wesolowski explains. "Estrogen production outside of the ovaries occurs by converting adrenal hormones such as testosterone or androstenediones into estrogen. That conversion is done by an enzyme called aromatase, so this class of agents called aromatase inhibitors decreases production of estrogen in peripheral tissues." But they also reduce bone density and can aid the development of osteoporosis, he says.

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What Can You Do?

Although some of the factors contributing to the development of osteoporosis and bone loss in breast cancer survivors are well beyond your control, there are a few things you can do that may help reduce the impact of these treatments.

First off, your doctor should take a bone density scan, called a DEXA scan, before you start any treatment protocol. "The DEXA scan is a low dose X-ray that basically allows a computer to measure the density of the bone," Wesolowski says. This scan will offer a baseline view of your bone density so your doctor can see how strong your bones are to begin with. Subsequent scans over the course of treatment can show any changes in bone density. "When we see a fairly rapid decrease in bone density, we initiate treatment of osteoporosis or treatment to prevent osteoporosis," he says.

And, as with most aspects of keeping yourself as healthy as possible while undergoing treatment for breast cancer, it's important to eat right and exercise. Both can help you maintain healthy bone density. "Exercise is beneficial not only for bone health but also, there have been studies showing that exercising on chemotherapy decreases incidence of nausea and improves the likelihood of completing the full course of chemotherapy," Wesolowski says. Weight bearing exercises that require your skeleton to do some work, such as walking, are considered best for improving bone density or at least slowing down the loss of bone.

"Another thing we recommend is adequate intake of calcium and vitamin D," Wesolowski says. For many Americans, this is apparently a challenge. A 2009 study published in the Journal of the American Medical Association found that 75 percent of American teenagers and adults had suboptimal levels of vitamin D in their blood. And a 2014 report from the Environmental Working Group estimated that 49 percent of American adults age 19 and older had a dietary intake of calcium below the estimated average requirement. (Vitamin D and calcium often travel together in discussions of bone health because vitamin D helps the body absorb calcium from dietary sources or supplements.)

[See: Breast Pain? Stop Worrying About Cancer.]

The National Osteoporosis Foundation recommends that adults under age 50 take 400 to 800 international units of vitamin D daily. For adults over age 50, that recommended intake level rises to 800 to 1,000 international units daily. For calcium intake, the NOF recommends that women aged 50 and younger take 1,000 milligrams of calcium per day while women aged 51 and older should strive for 1,200 milligrams of calcium daily.

Wesolowski says his patients may need slightly more of both micronutrients because of the breast cancer treatments they're receiving. He recommends 1,000 to 1,500 milligrams daily of calcium and 800 units per day for vitamin D, "divided into two doses each day. We typically recommend taking a commercially available combination 600-milligram calcium and 400-unit vitamin D tablet twice a day," he says.

However, some patients may not be able to tolerate calcium supplementation -- it can cause constipation or upset stomach in some people. If that's your situation, make sure you're getting enough calcium and vitamin D from your diet. Good sources of calcium and vitamin D include dairy products, fortified foods, egg yolks, dark, leafy greens, and fatty fish like tuna, salmon and mackerel.

Elaine K. Howley is a freelance Health reporter at U.S. News. An award-winning writer specializing in health, fitness, sports and history, her work has appeared in numerous print and online publications, including AARP.org, espnW, SWIMMER magazine and Atlas Obscura. She's also a world-record holding marathon swimmer with a passion for animals and beer. Contact her via her website: elainekhowley.com.