The Endocrine System’s Effects On Aging

By Aaron I. Vinik, MD, PhD, FCP, MACP, FACE with Mary Green

The many advances realized in modern medicine – enhanced diagnostic tools, more and better-targeted drug therapies, vaccinations against common killer diseases, and improved public health measures in areas such as nutrition and sanitation – have dramatically increased the average life span in the United States during the past century.

But healthful longevity with an excellent quality of life is the goal.

In consideration of the rapidly growing elderly population, examination of the endocrine system’s far-reaching effects in longevity and healthy aging deserve greater attention and understanding. Here we examine just a few of the many endocrine factors that impact the aging process and provide insight regarding interventions that can support moving through the golden years more gracefully.

Sarcopenia

Defined as age-related low muscle function (walking speed or grip strength) in the presence of low muscle mass (muscle wasting), the prevalence of sarcopenia varies widely, with estimates suggesting its presence in up to 13 percent of persons 60 to 70 years of age and up to 50 percent in those 80 years of age and older. It is one of the root causes of a host of health issues that plague the elderly, including physical frailty, hip fractures and other injuries. A prime example of sarcopenia is former worldclass bodybuilder and Governor of California Arnold Schwarzenegger. Although he claims to still work out daily, recent photos show the 70-year old Schwarzenegger’s body no longer has muscles that are full and solid – the muscles are wasted because of sarcopenia.

While there are common, non-endocrine causes of sarcopenia such as inactivity, weight loss without exercise, reduced blood flow and genetic factors, the muscles are supported by the endocrine system. And one of the major endocrine hormones that is important here is testosterone, which begins declining at the rate of 1 percent per year beginning around 30 years of age.

Another contributing factor to sarcopenia is insufficient leucine, a principal amino acid in the diet that stimulates the rate of protein synthesis and, thus, is critical to improving the integrity of muscle by slowing down the rate of muscle tissues degradation.

Growth hormone (GH) and insulin-like growth factor (IGF1), an endocrine hormone found naturally in your blood whose main job is to regulate the effects of growth hormone, also become insufficient as we age and are contributing factors to sarcopenia, as normal IGF-1 and GH functions include tissue and bone growth.

Diagnosing sarcopenia in the clinical setting can be achieved with a simple questionnaire called SARC-F (an acronym for strength, assistance in walking, rising from a chair, climbing stairs and falls, which asks: How much difficulty do you have in lifting and carrying 10 pounds?; How much difficulty do you have walking across a room?); How much difficulty do you have transferring from a chair or bed?; How much difficulty do you have climbing a flight of ten stairs?; How many times have you fallen in the last year?

Once sarcopenia has been identified, management and therapy is remarkably straightforward. While numerous studies have demonstrated that resistance exercise is the best primary treatment for sarcopenia, the key is providing individuals with options for movement that incorporate simple measures for strength and balance, that motivate them and that they will continue to stick to. For some it may be stretching bands, dancing or running, for others weight lifting or Tai Chi. The use of BOSU® balance-training balls and pilates to strengthen the core muscles are examples of worthwhile options.

Also, medical and nutritional therapy can be introduced. There is evidence suggesting that leucine-enriched essential amino acids, when taken in conjunction with an exercise regimen, will reduce sarcopenia. And the administration of testosterone in low doses can help build muscle mass, although it does not affect muscle strength.

Additionally, many elderly are insufficient in Vitamin D, which improves muscle function. Therefore, vitamin D replacement to achieve appropriate levels is recommended. Cell-based therapies to treat sarcopenias, such as repopulation with stem cells, may have potential in the future, but to-date have had success in the pre-clinical area only.

Thyroid Function With Advancing Age

Another area that deserves examination is the impact of the aging process on thyroid function.

With an increase in age, changes in thyroid hormone production, metabolism and action occur. Specifically, aging is associated with decreased secretion of thyroid-stimulating hormone (TSH), which is produced by the pituitary gland in the brain and directs the thyroid to make and release essential thyroid hormones T3 and T4 into the blood, where they travel to and are used by multiple target organs and systems. T3 and T4 secretions also are impaired as we age.

As a result of these changes, there is an increased prevalence of thyroid disease in the elderly, particularly what is known as sub-clinical thyroid disease, a disease that is not severe enough to present definite or readily observable symptoms. In general, subclinical thyroid disease is associated with an increased risk of overt thyroid disease.

The clinical signs of thyroid disease in the older population may be different that those observed in younger patients. For example, symptoms and signs that are typically hallmarks of an underactive thyroid — fatigue, weakness, constipation, reduced appetite, cold intolerance, hair loss and dry skin, for example — are more subtle and often attributed to the normal aging process.

As a result, identifying and appropriately treating thyroid diseases in elderly patients requires special attention, since symptoms can often manifest as a disorder of another system in the body, and are often influenced by a host of other concurrent conditions and factors, including medication that directly interferes with thyroid function.

For aging patients who have been diagnosed with overt hypothyroidism (underactive thyroid), treatment remains the introduction of hormone replacement therapy, which is the recommended treatment for hypothyroidism at any age. However, a more conservative approach is often used, with a lower starting dose of the replacement medication than younger adults might receive, as the replacement hormone might increase the risk of cardiac events such as angina pectoris (chest pain), irregular beating of the heart, or heart attack.

Likewise, the prevalence of hyperthyroidism (overactive thyroid) is increased in the elderly. As with hypothyroidism, the elderly usually lack the classic signs and symptoms typically seen in hyperthyroidism. Gastrointestinal issues and symptoms such as cognitive impairment, mania or depression can be signs of hyperthyroidism in the elderly. While surgery is a treatment option in younger patients, radioactive iodine treatment to destroy some of the thyroid tissue so that it will produce less thyroid hormone is a more convenient and effective treatment for the older patient. If this results in post-treatment hypothyroidism, hormone replacement medication can be administered.

Decreased Testosterone In Aging

While much has been researched and reported regarding hormone replacement therapy in older women, particularly the use of estrogen to lower the chances of death and disability from cardiovascular disease and osteoporosis, awareness of the decrease in testosterone levels that occurs with aging (referred to as gonadopenia) is a relatively recent phenomenon, gaining momentum over the last two decades as the elderly population expanded and patient interest in testosterone replacement therapy grew.

Produced primarily in the testicles, testosterone is responsible for maintain a male’s bone density, fat distribution, muscle strength and mass, facial and body hair, sex drive and sperm production.

It is widely known that testosterone concentrations decline with age. In fact, males achieve peak testosterone concentrations in their third decade of life, experiencing a 2 percent decline per year in testosterone after the age of 40 that continues throughout their lives. However, other factors such as obesity and type 2 diabetes can contribute to the decline. It is important to determine in older men if a low testosterone level is simply due to aging or if it is due to hypogonadism, a disease in which the body is unable to produce normal amounts of testosterone due to a problem with the testicles or with the pituitary gland that controls the testicles.

Although mainstream discussions of decreased testosterone in the aging male often focus on issues such as low sex drive and erectile dysfunction, symptoms related to low testosterone are numerous and varied and range from decreased muscle mass and reduced strength that can lead to physical frailty, depression, fatigue, difficulty concentrating and poor quality of life. And some studies have shown that low testosterone concentrations are associated with an increase in the incidence of cardiovascular disease and mortality.

There are a number of testosterone replacement therapy options available in the U.S. to improve symptoms and qualityof-life issues, among them injections, nasal formulations, and topical therapies such as patches and gels. Many small clinical trials have found that testosterone therapy in elderly men may increase their muscle mass, strength and physical functioning, as well as increasing bone mineral density at the hip and spine. However, concerns remain regarding lack of long-term data regarding whether the therapy increases the risk of prostate cancer or prevents cardiovascular issues. Thus, the risk-to-benefit ratio of testosterone therapy in elderly men is not yet clear.

Conclusion

There are many other endocrine system changes that occur with aging that significantly impact how we age and, thus, deserve greater attention — bone disease, growth hormone therapy, how to improve long-term outcomes in older persons with type 2 diabetes, the interaction of nutrition and metabolism. Those highlighted here are just a few.

As we become more focused on these changes and gain critical insight into the complex association between aging and the endocrine system, the valuable information produced by these efforts will help us enhance function in our aging patients and lead to not only a longer life, but a better quality of life.