Cortisol, Connective Tissue, Osteoporosis, and Arthritis
Aging, as most of us know all too well, is associated with dramatic changes in some of the structural aspects of our bodies, such as bone and muscle strength, skin elasticity, and joint function. Profound changes in body composition also accompany advancing age, so we progressively gain fat but lose muscle (sarcopenia), bone (osteopenia/osteoporosis), and joint cartilage (arthropenia/arthritis). This means we are likely to get weaker (due to having less muscle), feel tired (due to reduced aerobic endurance), and lose our ability to get around efficiently. Many people simply accept these changes as inevitable effects of the normal aging process—but they're not.
Luckily, researchers are learning more and more about the precise causes of age-related losses in connective tissues (muscle, bone, cartilage, skin, hair, and nails). While the cause of the aging of these tissues remains quite complex, scientists are narrowing down the list of potential mediating factors—and once again elevated cortisol levels are implicated as one of the primary markers for accelerating these tissue losses (along with low levels of anabolic hormones, such as estrogen in women and testosterone and DHEA in men).
Also fortunate is the fact that age-related loss of connective tissue can be reversed, even in individuals nearing a hundred years of age. Regular exercise programs incorporating strength training, with or without aerobic exercise, have been shown to preserve or increase amounts of muscle, bone, and cartilage in older adults, while also improving the ability to be independent. In addition, dietary factors such as maintaining a protein intake of up to one gram of protein per pound of body weight (see Chapter 7 for more detailed protein recommendations) and a calcium intake of at least fifteen hundred milligrams per day are well known to lead to positive benefits in terms of maintaining muscle and bone mass with age. The relationship between elevated cortisol levels and an accelerated loss of cartilage, bone, and muscle has been demonstrated in numerous situations, including cases of people with Cushing's syndrome (where elevated cortisol results in severe osteoporosis and arthritis) and anorexia nervosa (where elevated cortisol leads to bone and muscle loss). Studies such as these have also determined that curing these diseases, and thereby removing the source of excess cortisol production, also restores cartilage, bone, and muscle tissues. In experimental studies, cortisol has been shown to decrease levels of connective-tissue growth factors and inhibit the activity of bone-building cells (osteoblasts), muscle-building cells (satellite cells), and cartilage-building cells (chondrocytes). So here we have a situation in which excess cortisol levels not only accelerate the breakdown of connective tissues, but also interfere with the biochemical process of building and repairing those same tissues.
The same scenario of increased loss and suppressed repair is seen in related connective tissues, such as skin, hair, and nails. The actions of cortisol to enhance catabolism (breakdown) of many forms of connective tissues are well documented in the medical literature, and while these problems may not be of the same health magnitude as osteoporosis, nobody wants to have dry skin, thin hair, and cracked fingernails.
Most of us who have passed the age of forty have probably begun losing substantial amounts of muscle, bone, and cartilage, and our skin is a far cry from the soft, smooth stuff we were born with. We start to see these declines in connective-tissue quantity and quality starting in our mid-thirties and early forties, and by the time we're in our seventies, we're down about 20 percent from where we were in our twenties. These losses have all sorts of implications for how strong we are, how many calories we burn, how much energy we have, how we feel, and how we look. Elevated levels of cortisol as we age have been implicated in the acceleration of connective-tissue destruction, while declining levels of estrogen (in women), testosterone (in men), and IGF-1 and growth hormone (in both sexes) are known to be part of our hampered ability to rebuild damaged tissue.
The ability to rebuild damaged tissue plays a role in alleviating certain chronic pain conditions. Researchers at the University of Michigan have found that cortisol levels alone explained 38 percent of the variation in pain among patients with fibromyalgia, while scientists in Hong Kong have shown that optimism is able to reduce cortisol levels and perception of pain to a greater degree than pessimism and that negative thoughts can increase cortisol and subjective pain.
Greek researchers from the Athens Medical School have shown that high stress and cortisol levels not only increase inflammation throughout the body (via higher levels of cytokines), but also suppress thyroid-hormone metabolism. Suppressed thyroid function results in reduced levels of the active T3 form of thyroid hormone (which helps to maintain the body's metabolic rate) and increased levels of inactive rT3 (reducing the number of calories the body burns). And, as if a rise in inflammatory cytokines weren't bad enough for causing an increase in your risk for heart disease, researchers from the University of Alberta have also shown that cytokines stimulate cortisol activation by HSD, and thus may serve as the primary signal for inflammation-induced abdominal fat gain.
The good news in terms of connective-tissue maintenance is that a series of studies conducted at Tufts University and Penn State University have shown dramatic benefits in countering the frailty that is associated with extreme muscle, cartilage, and bone loss in the elderly. Results from these studies show that frail elderly participants are able to increase muscle and bone mass and double their muscle strength with resistance training performed two to three times a week. Participants in the exercise programs were able to get around more easily and with less joint pain than they could prior to the training. An interesting side benefit of the added muscle was an average 15 percent increase in daily caloric expenditure when compared to sedentary participants.
It's a bit harder to assess the effects of elevated cortisol levels on other connective tissues in humans, such as skin, hair, and nails. However, laboratory studies have shed some interesting light on the fact that excess cortisol bears a wide range of adverse effects on the underlying biochemistry of the skin and related tissues. For example, researchers in Finland have shown that while a low level of cortisol is able to stimulate the synthesis and slow the breakdown (by about 25 percent) of structural skin elements such as hyaluronan and proteoglycans, higher levels of cortisol have exactly the opposite effect, reducing synthesis and accelerating degradation of these compounds by more than 40 percent. Both hyaluronan and proteoglycans are responsible for hydrating the skin by attracting and holding adequate amounts of moisture, so reduced levels of these compounds in the skin mean that the skin dries out. Similar effects have been noted for related skin proteins, such as elastin (needed for skin elasticity) and collagen (needed for skin strength), and these observations have led many researchers to hypothesize that elevated cortisol levels may be responsible for accelerated skin “aging” and the overall skin atrophy (wrinkling) observed during drug treatment with synthetic cortisol.