Ask the average American man what his greatest
health concerns will be as he ages, and his answer
would likely be drawn from a familiar list: heart
disease, prostatic hyperplasia, prostate cancer,
osteoarthritis, erectile dysfunction. Few would list
osteoporosis, the degenerative skeletal condition that is generally
considered a “woman’s disease.” Most would be surprised
to learn that the prevalence of male osteoporosis is close to that
of prostate cancer; about 20 percent of the 10 million Americans
with osteoporosis are men. Men account for over a quarter of
all osteoporotic fractures annually. It is estimated about 25 percent
of men will suffer an osteoporotic fracture in their lifetime,
more than the estimated 16 percent that will be diagnosed with
prostate cancer. Yet, male osteoporosis remains a relatively over
looked condition that is poorly understood amongst men. For
example, on the National Health and Nutrition Examination
Survey (NHANES) only one percent of male survey takers over
65 reported they had osteoporosis; bone mineral density (BMD)
testing revealed that four times as many actually had the disease.
In this article, we will briefly discuss the progression of male
osteoporosis, its specific risk factors, and potential treatments.What is Osteoporosis?
Osteoporosis describes a condition of improperly or incompletely
crystallized bone tissue. This results from an imbalance
in bone remodeling. Remodeling is a critical process in bone
metabolism that involves the removal (resorption) of older bone
tissue and its replacement with an equivalent amount of pristine
bone at the same site. Remodeling becomes an important
mechanism for repairing damage from repeated stress on the
skeleton, and is vital for removing older bone tissue, which has
lost its resilience. Resorption also serves as a means for releasing
calcium or phosphorous when there is a dietary deficiency.
Bone remodeling continues in such a fashion that most of the
adult skeleton can be replaced about once per decade.
The maintenance of a static density and mass of bone depends on the balance of bone synthesis by bone-building cells (osteoblasts) and bone-resorbing cells (osteoclasts). Equivalent levels of activity by both cellular processes allows for consistent bone remodeling and the optimization of the bone’s physical properties. A shift of this equilibrium towards synthesis adds new bone; a shift towards resorption results in net bone loss. If bone resorption were to progress unchecked, or if the bone formation process were somehow hindered, then bone would begin to lose minerals, leaving porous bone matrix. The less-dense “spongy” bone (trabecular bone) that predominates in the wrist, spine, and hip becomes thinner and weaker, with less mechanical strength and a higher probability of fracture.
For practical purposes osteoporosis is defined as bone mineral density (BMD) of more than 2.5 standard deviations below the mean for a 30 year old individual of the same sex and ethnicity (called the T-score), which translates to a bone mass approximately >30 percent less than average. A pre-osteoporotic state of low bone mass (traditionally referred to as osteopenia), describes a BMD that ranges 10 – 30 percent below average and has some increased risk of fracture. The most common osteoporotic fractures are those of the spine (27 percent of all fractures); common non-vertebral fractures occur at the wrist (19 percent), hip (14 percent) and pelvis (7 percent). These fragility fractures are responsible for decreased quality of life due to pain and loss of mobility. Hip fractures are especially problematic; they increase the risk of additional hip or vertebral fractures by over two-fold, and about half of patients experiencing hip fracture will experience long-term loss of mobility. Hip and vertebral fractures also carry an increased risk of mortality, especially in men. Within six months of a hip fracture, the mortality rate is about 10 – 20 percent; about one-third of men will die within a year of hip fracture. Loss of independence is also more likely in men who survive hip fractures than in women.
Primary and Secondary Causes of Osteoporosis in Men
Primary osteoporosis is the cumulative loss of bone mass
with age, as one experiences changes in sex hormone levels.
Although men do not usually experience a sudden decrease in
sex hormone production as do women during menopause, levels
of testosterone in men begin to decrease as early as age 30,
and can drop at a rate of 0.8 percent per year. Testosterone, one
of the main androgens in men, is responsible for regulating not
only secondary sexual characteristics, but also body composition,
including lean body mass and bone mineral density. Like
estrogen, testosterone signals osteoblasts to build new bone,
while inhibiting the bone-resorption by osteoclasts. Androgens
also stimulate the mineralization of bone, and indirectly stimulate
the mechanical loading of bone (the stress on the skeleton,
as experienced during exercise, that increases the synthesis of
new bone). Low testosterone levels, not surprisingly, are associated
with increased prevalence of osteoporosis and greater
fracture incidence (particularly of the hip) in older men. Testosterone
is also a source of estrogens in men (by conversion
through the activity of the enzyme aromatase); low estrogen
levels in men are also associated with lower bone mass.
As is the case for women, low body weight, smoking, Caucasian race, limitations in physical activity, and history of previous fractures are also risk factors for primary osteoporosis in men. Inadequate calcium consumption, increased calcium excretion, and insufficient serum vitamin D levels are additional well-established risk factors for primary osteoporosis. Other dietary risk factors, such as soft drink consumption, low phosphorus, and high dietary acid load are beginning to gain more attention for their ability to push bone metabolism towards resorption in women; it is not unreasonable to expect these factors may present risks in men as well.
Secondary osteoporosis results from specific medical conditions, diseases, or medication use. Although less common in women (20–30 percent of cases), secondary osteoporosis may account for over half of the cases in men. Frailty fractures or low BMD in younger and middle-aged men can be indicative of this disease. Most causes of secondary osteoporosis are similar between the sexes, and include endocrine disorders (diabetes and hyperthyroidism), gastrointestinal disorders that interfere with nutrient absorption (bariatric surgery has emerged as a condition which may double fracture risk), chronic inflammatory diseases (such as rheumatoid arthritis or lupus), and certain medications (particularly glucocorticoids and immunosuppressive drugs). Male hypogonadism (sudden drops in androgen levels) is a major risk factor for secondary osteoporosis, likely through the mechanisms mentioned above. Hypogonadism is a common side effect of the androgen-deprivation therapies that are the mainstay of prostate cancer treatments, and can result in significant bone loss. Alcohol abuse may be a more prevalent risk factor for decreased BMD in men than in women; low bone mass is common in men who seek medical help for alcohol abuse. Moderate alcohol consumption (perhaps up to 29 g/day; there is not a real definition for “moderate”), however, has been associated with a healthy BMD in multiple studies.
Treatment of Osteoporosis in Men
Despite its prevalence, osteoporosis in men has been relatively
overlooked by researchers; therefore, most of our understanding
of the disease has been derived from studies of the disease
in women. Accordingly, studies of osteoporosis treatments in
men are smaller and fewer in number than those in women.
Calcium and vitamin D supplementation, often in conjunction
with bisphosphonate drugs, has been the standard protocol
for treatments of primary and secondary (hypogonadal men or
those on androgen-deprivation therapy) osteoporosis. Testosterone
supplementation therapy has been proven effective at
increasing BMD in hypogonadal men, but requires consistent
monitoring for increases in hormone-related cancer risk. Nutritional
and lifestyle modifications (such as increased exercise
and smoking cessation) are important practices for lowering
fracture risk. It is unclear whether the bone-promoting activities,
other well-characterized nutrients (such as the K vitamins,
potassium, or trace minerals like silicon, boron, and manganese)
will be as effective in men as they have been in women;
this is certainly an important area for future scientific study.
Summary
Osteoporosis in men, although surprisingly common, is a
frequently overlooked consequence of the aging process. It
shares many of the same causes and risk factors as it does the
condition in women. Secondary causes of osteoporosis (particularly
prostate cancer therapies and alcohol abuse) are a more
common cause of the disease in men, and require additional
considerations for their successful management. It is hoped
as male osteoporosis becomes more recognized and better
understood amongst practitioners and patients, research into
its causes and effective treatment will increase accordingly.
