Over the past couple of months we've discussed many of the biggest risk factors associated with some of the leading causes of death in the United States -- heart disease, cancer and stroke. Today I want to turn the tables a bit and look at a disease that affects an equally large number of people. While it may not in itself be deadly, it can make a person's life miserable if it isn't properly dealt with. The disease: osteoporosis.

Osteoporosis is a condition whereby a person's bones become so brittle and frail that they can break or fracture from a fall to something as simple as a heavy cough. The condition, in its simplest form, arises because the body is unable to make new bone tissue faster than the rate at which the body is absorbing old bone tissue. While osteoporosis can occur anywhere, it's most common in the wrist, hip, and spine.

According to the National Institutes of Health, more than 40 million people either have osteoporosis, or are at a higher risk of developing the disease because of low bone mass.

Figures in percentages for persons surveyed over 50 years of age. Source: Center for Disease Control and Prevention, National Health and Nutrition Examination Survey 2005-2008. 

When both the femur and spine are taken into account, roughly one in two respondents (49%) over age 50 in a CDC and National Health and Nutrition Examination Survey were found to have low bone mass, which is an early-stage warning for developing osteoporosis. That represents a huge opportunity for the pharmaceutical industry, but it also serves as a wake-up call to the rest of us to do what we can to avoid the biggest risk factors of the disease.

According to the Mayo Clinic, there are five big risk factors that people should be watching out for if they'd like to reduce their chances of developing osteoporosis.

1. Genetic factors
Whereas the majority of factors on the Mayo Clinic's list can be altered by lifestyle changes, your genetic make-up is unfortunately not one of those. Women, for instance, are more prone to developing osteoporosis than men, particularly because of their smaller bone structure. Particular races also tend to be more prone to developing the disease, such as women of Caucasian and Asian descent. Similarly, having a family member with a history of osteoporosis will put you at a greater risk of developing the disease. Finally, we can't control the fact that we're getting older, no matter how many 29th birthday anniversaries we have (I should know, as I've had a few), and age is a primary risk factor in developing osteoporosis.

2. Hormone levels
One of the bigger risk factors for both women and men as they age is a decline in their sex hormone levels -- estrogen for women and testosterone for men. It has been shown that a decline in these hormones can lead to bone deterioration and thus put a person at a greater risk of developing osteoporosis.

The good news is that there are plenty of options to counteract the decline in estrogen for women and testosterone for men; however, physicians don't often recommend utilizing estrogen solely to counteract bone loss in women. Men, however, have FDA-approved Androgel 1.62%, made by AbbVie (ABBV 1.26%), to fall back on. Androgel is prescribed for men who have zero to low testosterone production, and, among other things, it can help improve bone mineral density. Through the first six months of the year Androgel was AbbVie's second best-selling drug at $498 million in cumulative sales and could be in line for future growth as baby boomers continue to age.

3. What you eat
If you haven't noticed by now, what you eat can play a big role in whether you develop a type of disease. Even in cases where the cause of a disease isn't completely known, such as in osteoarthritis, poor diet is often blamed as an exacerbating factor that can increase your risk of developing a disease. In terms of osteoporosis, diets that are low in calcium can result in early-life bone loss. Extenuating factors can also affect your bone density, such as whether you've had some form of gastrointestinal surgery, or if you have anorexia, an eating disorder that starves the body of numerous nutrients, including calcium.

Specifically, vitamin D and calcium intake are the two most important dietary factors as it relates to reducing your risk of osteoporosis. Vitamin D is a crucial component to calcium absorption in the intestines. Fish, many cereals, eggs, and several dairy products (including milk), serve as excellent sources of vitamin D. You can also get it from exposure to the sun. Calcium, which is one of the primary building blocks of our bones, is often found in low-fat milks and cheeses, as well as dark leafy green vegetables. 

4. Other medications
The downside of taking medication to treat one ailment is that it sometimes can have side effects that can cause you to develop another. Certain types of medications that are used to treat depression, cancer, gastric reflux, and seizures have been known to increase a patient's chances of developing osteoporosis.

One commonly prescribed medication that comes with such a warning is Novartis' cancer drug Femara for the treatment of early-stage breast cancer. Based on its indications when it was approved in 2005, patients on Femara were about 42.5% more prone to fracturing than those on the placebo (5.7% versus 4%). Despite its various adverse effects, few if any of these side effects have had any effect on the overall sales of the drug.

5. Lifestyle choices
You know the old adages that you should "eat right," "get out and exercise," and "drink in moderation"? Well, this is one of those cases where your advice-givers were spot-on. People who live a relatively sedentary lifestyle, consume alcohol often, and use tobacco (smoking or chewing tobacco) are more susceptible to developing osteoporosis. Of the five risk factors, this is among the easiest to change.

Where we are right now in osteoporosis care
For those who can make certain lifestyle choices -- including proper diet, exercise, and a moderation or elimination of tobacco or alcohol use -- the probability of developing osteoporosis during their lifetime should be reduced. For others who are genetically predisposed to a higher risk of the disease, or already have the disease, medical improvements are needed.

There are a number of FDA-approved bone-strengthening/fracture-reducing medications available. The most commonly prescribed treatments are a drug class known as bisphosphonates. Warner Chilcott's (NASDAQ: WCRX) Actonel belongs to this class of drug, which is often prescribed as a long-term solution to reducing bone depletion and fracturing. Unfortunately, recent studies have shown that over time, bisphosphonate usage can cause cracking of the thigh bone, as well as cause jaw bone cancer in rare cases. Warner Chilcott has needed to defend itself on multiple occasions in cases where Actonel has been alleged as a cause of death relating to jaw bone cancer.

For women, selective estrogen receptor modulators, or SERMs, are another possible option. One of the best-known SERM's is Eli Lilly's (LLY -0.14%) Evista, which actually serves the dual function in post-menopausal women of treating osteoporosis and reducing the risk of contracting invasive breast cancer. Through the first six months of 2013, Evista has brought in $519 million in sales, putting it once again on track to bring in about $1 billion in annual revenue.

If neither of these treatments can be tolerated (not everyone can handle taking bisphosphonates), Amgen's (AMGN -0.71%) Prolia is another option for post-menopausal women. Designed to treat the thinning of bones, Prolia is given as an injection just twice a year for women at high risk for bone fractures. On paper, the prospect of just two shots a year sounds considerably more pleasant than taking pills year-round, but the side effects for Prolia can be just as unpleasant as, if not more unpleasant than, long-term bisphosphonate use, including the potential for hypocalcemia, severe allergic reactions and infections, jaw bone complications, and thigh bone fractures.

Where we're headed
As we've often seen, spearheading new treatment options in chronic therapies doesn't always guarantee success. In fact, Amgen and UCB discontinued a midstage study of fracturing-resistant experimental drug romosozumab in February after the top-line data painted a picture that didn't seem optimal for ongoing clinical study.  

One drug in particular, however, looks as if it's poised to take on osteoporosis head-on, perhaps as soon as next year. The drug, odanacatib, which Merck (MRK 0.24%) is developing, had its late-stage trial stopped early by an independent monitoring committee because it was working so well. Whereas most bisphosphonates reduce fracturing by approximately 35%, Wall Street analysts suspect that when we finally get to see all of the data that odanacatib may reduce fracturing by more than 40%. Merck, in order to address whatever safety concerns remain surrounding odanacatib, is also running an ongoing safety extension trial and, barring good results, plans to file for a new drug application in early 2014. Early estimates place odanacatib's peak sales around $3 billion.

The bottom line
Don't be surprised if you see additional biopharmaceuticals focused on this chronic disease, but do understand that there are lifestyle choices you can make to lower your risk of developing osteoporosis.

From an investing perspective, it's also clear that osteoporosis prevention is going to become a hotbed of R&D as the baby boomer population ages. Merck definitely has the clear path to success at the moment, but don't discount the ease-of-use for Amgen's Prolia, either, which may come with a few added complications but is by far the easiest to use.