Normal Age-Related Changes in Thyroid Hormone Economy

Age-Related Resistance to Thyroid Hormone Action

The age-related resistance to thyroid hormones (THs) explains the paucity of symptoms and signs of hyperthyroidism in older adults and may partly explain the myriad of symptoms and signs of hypothyroidism in biochemically euthyroid older people. This review considers the available data on the mechanisms underlying TH resistance with aging and compares these physiologic changes with the changes observed in congenital TH resistance syndromes. Aging is associated with alterations in TH economy along with a host of changes in the responsiveness of various tissues to THs. The age-related resistance to THs can be attributed to decreased TH transport to tissues, decreased nuclear receptor occupancy, decreased activation of thyroxine to triiodothyronine, and alterations in TH responsive gene expression. Although an increase in serum TH levels is expected in syndromes of TH resistance, unchanged serum TH levels in the euthyroid elderly is the result of increased sensitivity to TH negative feedback with increased suppression of thyroid-stimulating hormone, decreased thyroidal sensitivity to thyroid-stimulating hormone, and decreased TH production and secretion. The current clinical evidence suggests that the age-related TH resistance is mostly an adaptive response of the aging organism. It is tempting to speculate that similar changes can occur prematurely in a group of younger people who present with signs and symptoms of hypothyroidism despite normal serum thyroid function tests.

Influence of thyroid hormone therapy on the fracture rate - A claims data cohort study

INTRODUCTION

It has been debated for years whether long-term thyroid hormone intake causes fractures. Not only have previous studies suffered from design limitations, they also reached contradictory conclusions. We investigated thyroid hormones (thyroxine) as a possible risk factor for fractures in a cohort of 6.7 million persons based on administrative data.

METHODS

The database consists of anonymized settlement data of approximately 70 German statutory health insurances covering a time period of six years. All subjects aged 60 and above were included in the study; subjects with repeated thyroxine prescriptions were assigned to the exposure group; members without thyroxine prescriptions to the control group. Outcome was any incident fracture during a declared time period. In order to calculate fracture risk, we performed multivariate cox regression analyses to adjust for confounders.

RESULTS

Of 798 770 subjects fulfilling the inclusion criteria, 11.7% took thyroxine regularly and belong to the exposure group. The final cox regression showed that subjects taking thyroxine have a 6.3% higher risk (HR 1.063; CI 1.046-1.080, p=<.0001) than members of the control group.

DISCUSSION

The study supports the assumption that long term thyroxine intake leads to an increase in fracture risk among patients older than 60years. The findings have implications for long term thyroxine treatment.

Thyrotropin levels within the lower normal range are associated with an increased risk of hip fractures in euthyroid women, but not men, over the age of 65 years

CONTEXT

The contemporary literature on the relationship between serum TSH levels and osteoporotic fractures in euthyroid individuals is limited by conflicting results and analyses conducted on a small number of fractures.

OBJECTIVE

Our objective was to examine the association between the normal range of variation of TSH and the incidence of hip fractures in male and female euthyroid patients aged 65 years or older.

DESIGN AND SETTING

We performed a population-based historical prospective cohort study within the Clalit Health Services population.

PARTICIPANTS

Clalit Health Services members aged ≥65 years with at least 1 TSH measurement during the year 2004. We excluded patients with preexisting hip fracture, thyroid disease, malignancy, or chronic kidney disease.

OUTCOME MEASURES

The primary outcome was hip fracture, and the secondary outcome was any other osteoporotic fracture.

STATISTICAL ANALYSIS

Adjusted odds ratios comparing episodes of each outcome across 3 TSH groups (low, 0.35-1.6 mIU/L; intermediate, 1.7-2.9 mIU/L; high, 3-4.2 mIU/L) were generated using logistic regression models.

RESULTS

The 14 325 included participants suffered from 514 hip fractures (mean follow-up, 102 ± 3 months). Women, but not men, in the lowest TSH group had a higher incidence of hip fractures (odds ratio = 1.28, 95% confidence interval = 1.03-1.59, P = .029) when compared with the intermediate group, after multivariate adjustment for age, comorbidities, and use of drugs affecting bone metabolism. There was no difference in hip fracture incidence between intermediate- and high-TSH groups. No association was found between TSH levels and other osteoporotic fractures.

CONCLUSIONS

TSH levels within the lower normal range are associated with an increased risk of hip fractures in euthyroid women, but not men, aged 65 years and more.

Unique Aspects of the Elderly Surgical Population: An Anesthesiologist's Perspective

Increasing life expectancies paired with age-related comorbidities have resulted in the continued growth of the elderly surgical population. In this group, age-associated changes and decreased physiological reserve impede the body's ability to maintain homeostasis during times of physiological stress, with a subsequent decrease in physiological reserve. This can lead to age-related physiological and cognitive dysfunction resulting in perioperative complications. Changes in the cardiovascular, pulmonary, nervous, hepatorenal, endocrine, skin, and soft tissue systems are discussed as they are connected to the perioperative experience. Alterations affect both the pharmacodynamics and pharmacokinetics of administered drugs. Elderly patients with coexisting diseases are at a greater risk for polypharmacy that can further complicate anesthetic management. Consequently, the importance of conducting a focused preoperative evaluation and identifying potential risk factors is strongly emphasized. Efforts to maintain intraoperative normothermia have been shown to be of great importance. Procedures to maintain stable body temperature throughout the perioperative period are presented. The choice of anesthetic technique, in regard to a regional versus general anesthetic approach, is debated widely in the literature. The type of anesthesia to be administered should be assessed on a case-by-case basis, with special consideration given to the health status of the patient, the type of operation being conducted, and the expertise of the anesthesiologist. Specifically addressed in this article are age-related cognitive issues such as postoperative cognitive dysfunction and postoperative delirium. Strategies are suggested for avoiding these pitfalls.

Trauma in the elderly: considerations for anesthetic management

The volume of geriatric trauma patients is expected to increase significantly in coming years. Recognition of severe injuries may be delayed because they are less likely to mount classic symptoms of hemodynamic instability. Head injuries of any severity may place geriatric patients at increased risk of mortality, but there are currently no geriatric-specific treatment recommendations that differ from usual adult guidelines. Our understanding of best practices in geriatric trauma and anesthesia care continues to expand, as it does in all other areas of medicine.

Age-related changes in renal and hepatic cellular mechanisms associated with variations in rat serum thyroid hormone levels

Aging is associated with changes in thyroid gland physiology. Age-related changes in the contribution of peripheral tissues to thyroid hormone serum levels have yet to be systematically assessed. Here, we investigated age-related alterations in the contributions of the liver and kidney to thyroid hormone homeostasis using 6-, 12-, and 24-mo-old male Wistar rats. A significant and progressive decline in plasma thyroxine occurred with age, but triiodothyronine (T(3)) was decreased only at 24 mo. This was associated with an unchanged protein level of the thyroid hormone transporter monocarboxylate transporter 8 (MCT8) in the kidney and with a decreased MCT8 level in the liver at 24 mo. Hepatic type I deiodinase (D1) protein level and activity declined progressively with age. Renal D1 levels were decreased at both 12 and 24 mo but D1 activity was decreased only at 24 mo. In the liver, no changes occurred in thyroid hormone receptor (TR) TRalpha(1), whereas a progressive increase in TRbeta(1) occurred at both mRNA and total protein levels. In the kidney, both TRalpha(1) and TRbeta(1) mRNA and total protein levels were unchanged between 6 and 12 mo but increased at 24 mo. Interestingly, nuclear TRbeta1 levels were decreased in both liver and kidney at 12 and 24 mo, whereas nuclear TRalpha(1) levels were unchanged. Collectively, our data show differential age-related changes among hepatic and renal MCT8 and D1 and TR expressions, and they suggest that renal D1 activity is maintained with age to compensate for the decrease in hepatic T(3) production.

Evaluation of neuroendocrine status in longevity

It is well known that physiological changes in the neuroendocrine system may be related to the process of aging. To assess neuroendocrine status in aging humans we studied a group of 155 women including 78 extremely old women (centenarians) aged 100-115 years, 21 early elderly women aged 64-67 years, 21 postmenopausal women aged 50-60 years and 35 younger women aged 20-50 years. Plasma NPY, leptin, glucose, insulin and lipid profiles were evaluated, and serum concentrations of pituitary, adrenal and thyroid hormones were measured. Our data revealed several differences in the neuroendocrine and metabolic status of centenarians, compared with other age groups, including the lowest serum concentrations of leptin, insulin and T3, and the highest values for prolactin. We failed to find any significant differences in TSH and cortisol levels. On the other hand, LH and FSH levels were comparable with those in the elderly and postmenopausal groups, but they were significantly higher than in younger subjects. GH concentrations in centenarians were lower than in younger women. NPY values were highest in the elderly group and lowest in young subjects. We conclude that the neuroendocrine status in centenarians is markedly different from that found in early elderly or young women.

Assessment of age-related morphological and functional changes of selected structures of the head and neck by computed tomography, magnetic resonance imaging, and positron emission tomography

The head and neck is a complex anatomical region that can be evaluated using many imaging modalities. It is important to discern normal structures from ones that are affected by disease and to study how these structures change in their morphological and functional properties with aging. Therefore, using magnetic resonance imaging (MRI), we retrospectively evaluated volumes of the parotid glands, submandibular glands, thyroid gland, tongue, soft palate, and lingual tonsils in 64 subjects ages 13 to 81 years. Volume, attenuation (HU), and metabolic activity (maximum SUV) of the parotid, submandibular, and thyroid glands were assessed retrospectively using positron emission tomography/computed tomography (PET/CT) imaging in 35 subjects ages 10 to 76 years. Metabolic activity (maximum SUV) of the parotid, submandibular, and sublingual glands; tongue; adenoids; and tonsils (lingual and palatine) were evaluated retrospectively using PET imaging in 15 subjects ages 6 to 20 years. Metabolic volumetric products of the parotid, submandibular, and thyroid gland were calculated and analyzed with increasing age in subjects who underwent PET/CT imaging. Structures that exhibited statistically significant changes (P < 0.05) with increasing age included the submandibular glands, thyroid gland, soft palate, and adenoids. The CT volume of the submandibular glands increased with age, and the attenuation decreased with age with statistical significance. The thyroid gland volume, as measured using MRI, showed a statistically significant decrease with aging. The volume of the soft palate and lingual tonsils, as measured by MRI, exhibited a statistically significant decrease in volume with aging. The maximum SUV of the adenoids demonstrated a statistically significant decrease with aging. In conclusion, CT, MRI, and PET may be used to quantitatively and qualitatively assess structures of the head and neck and are useful in the assessment of structural and functional changes of these structures with aging.

Geriatric trauma: special considerations in the anesthetic management of the injured elderly patient

Modern society is characterized as having an ever enlarging population of older adults. There are more elderly patients, and the average age of this group is increasing. The anesthetic management of surgery for the elderly trauma victim is more complicated than in younger adults. Evaluation of the physiologic status of the geriatric patient should take into account the variability of the changes associated with advancing age. Care of the injured elderly patient requires thorough preoperative assessment and planning and the involvement of a multidisciplinary clinical team knowledgeable about and interested in the management of the elderly surgical patient.

Potential role of high serum leptin concentration in age-related decrease of fatty acid synthase gene expression in rat white adipose tissue

Ageing in rats is associated with significant reduction of lipogenic enzymes genes expression and the rate of fatty acids synthesis in white adipose tissue. Since resistance to insulin and/or triiodothyronine is not directly related to reduction in lipogenic enzymes activity in white adipose tissue of old rats, we have proposed recently that the age-related increase in leptin gene expression and high serum leptin concentration could, at least partly, account for the down regulation of lipogenic enzymes gene expression. To test this hypothesis, in this paper we experimentally (by single intraperitoneal injection of recombinant leptin) increased plasma leptin concentration in young rats to the level observed in old animals, and we examined its effect on fatty acids synthase (FAS) gene expression in white adipose tissue. The results presented in this paper indicate that leptin administration to young rats, in amount that cause the increase in serum leptin concentration to that found in old rats, significantly decreased the white adipose tissue FAS gene expression. We propose, therefore, that leptin could play a causative role in the down-regulation of lipogenic enzyme gene expression observed with ageing.

Endocrine alterations in the aging male

The recent increase in the elderly population, current health trends and awareness of age-related changes in the male endocrine system, have led to discussions about the role of the hormonal changes in the aging process in males. Better prevention and treatment of suboptimal health status and age-related diseases in aging men are based on an improved understanding of aging, particularly of the significance of age-associated hormonal changes. The aims of this study were 1) to evaluate the age dependence of the serum concentrations of the following important hormonal parameters in adult males using the IMMULITE 1 automated assay system (DPC, Los Angeles): testosterone, dehydro-epiandrosterone sulfate (DHEAS), estradiol (E2), sex hormone binding globulin (SHBG), lutropin (LH), follitropin (FSH), cortisol, prolactin, thyroid stimulating hormone (TSH), free triiodothyronine (fT3), free thyroxine (fT4) and the growth hormone-dependent parameters insulin-like growth factor (IGF-I) and IGF-binding protein-3 (IGFBP-3) and 2) to derive the following parameters: calculated free testosterone (cFT), ratio of calculated free testosterone to total testosterone (% cFT) and free androgen index (FAI). We found a significant decrease between the 21-30-year age group and the > 70-year age group for total testosterone (-42.4%), FAI (-65.5%), cFT (-60.0%), % cFT (-30.0%), DHEAS (-71.9%), E2 (-35.4%), TSH (-23.6%), IGF-I (-40.3%) and IGFBP-3 (-26.5%). Since the decreases in the FAI and cFT were greater than that of total testosterone and because these derived parameters reflect the biologically active fraction of testosterone, FAI and cFT are better markers for androgen deficiency in males. In contrast, a significant increase with age was observed for SHBG (+61.2%), LH (+40.0%), FSH (+98.3%) and cortisol (+54.2%). No significant alterations with age were observed for prolactin, fT3 and fT4. The study demonstrates that determining complete profiles of the androgenic, gonadotropic, adrenocortical, thyroid, pituitary and growth hormone/IGF endocrine axes in middle-aged and elderly men may be helpful in obtaining a correct clinical diagnosis for various hormonal disorders.

Management of Obesity in the Elderly

Over the last few decades, there has been an unprecedented increase in the prevalence of obesity, especially in economically developed countries. Furthermore, it is becoming an increasingly recognized health problem in the elderly. The precise mechanisms underlying increased adiposity in the elderly are not known. Aging is associated with a host of biologic changes that limit the ability of the individual to regulate energy homeostasis. Thus, it is likely that older individuals may be more likely to develop the two extremes of the spectrum of nutritional abnormalities, namely malnutrition and increased adiposity. These nutritional abnormalities are associated with significant morbidity and mortality. Current guidelines define overweight as a body mass index (BMI) of 25-29.9 kg/m2 and obesity as a BMI of 30 kg/m2 or more. However, the optimal BMI may be different in older individuals. Management strategies should attempt to optimize the nutritional status of older individuals. Age per se cannot be used as a justification for denying medical management of obesity to elderly individuals. Individualized programs with the goal of achieving modest weight reduction in obese patients are likely to result in immediate (e.g. alleviation of arthritic pains and reduction of glucose intolerance) and possibly long-term (e.g. reduction in cardiovascular risk) healthcare benefits. Management should emphasize lifestyle modifications, while the use of pharmacologic agents such as sibutramine and orlistat should be reserved for select groups of patients who do not respond to lifestyle modification.

The Endocrinology of Aging

Physiologic systems have substantial reserves in younger individuals. The process of aging and intercurrent pathologic processes gradually eliminate these reserves. Changes in endocrine systems, including menopause in women, androgen deficiency in men, loss of skeletal mass, decrease in growth hormone serum concentrations, and increased incidence of type 2 diabetes are all more common or certain in older individuals. This review summarizes the progression of each of these processes with age, the potential outcomes of the untreated process, and the treatment outcomes for these age-related losses. Maintenance of a premenopausal lipid profile presumably protects against cardiovascular events. Maintenance of skeletal mass reduces fracture risk and risk for loss of mobility and independence. Testosterone replacement in hypogonadal older men improves strength and presumably function and independence. Growth hormone therapy is reported to have similar effects. Improvement of long-term outcomes in older type 2 diabetics, however, is more difficult to demonstrate.

The age-related changes in lipogenic enzymes: the role of dietary factors and thyroid hormone responsiveness

To determine whether resistance to insulin or to thyroid hormones rather than an inherent defect in enzyme activity expression account for the age-related changes in lipogenic enzymes, the activities of malic enzymes (ME), fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G-6PD) and 6-phosphogluconate dehydrogenase (6-PGD) were assayed in hepatic, retroperitoneal fat and epididymal fat cytosol of male Fischer 344 rats at 3.5, 12 and 25 months of age. The rats were maintained on either regular rat chow with 62% of calories as complex carbohydrates or were given either high glucose or fructose diet with 65.7% of calories provided by glucose or fructose respectively. Additional groups of young and aged rats were treated with L-triiodothyronine (T3) (15 microg/100 g body weight) for 10 days. Treatment with T3 resulted in higher levels of hepatic ME activity regardless of the diet consumed or the age of the rats. T3 had no consistent effect on FAS, G-6PD or 6-PGD activities. ME response to T3 in young rats was significantly greater than that found in aged rats regardless of diet. The age-related decrease in basal hepatic ME activity was not apparent in rats maintained on the high glucose or the high fructose diets, yet the T3 responsiveness of ME in rats maintained on these diets was not normalized. In adipose tissue, with the exception of the age-related changes in basal activity of the lipogenic enzymes, neither T3 nor the feeding of the test diets had any consistent effects. Since insulin resistance induced by high fructose feeding did not reduce hepatic lipogenic enzymes, it is unlikely that the age-related increase in insulin resistance explains the reduced lipogenic enzyme activity in aged rats. However, resistance to thyroid hormone action found in aged rats may partly account for the reduced hepatic lipogenic enzyme activity.

Pituitary tumours in the elderly

Pituitary tumours in the elderly are a neglected topic in the literature of endocrinology and gerontology. Data from autopsy studies in the elderly show that the commonest tumours are microadenomas, which are either immunocytochemically negative or stain for prolactin. Prolactin-secreting pituitary tumours, however, appear rarely in clinical series of patients in this age group and non-functioning adenomas are the commonest tumour seen, although pituitary metastasis and craniopharyngiomas also occur. Diagnosis can be difficult, but the commonest presentation is visual field loss. Hypopituitarism may be diagnosed late and incidental radiological diagnosis is not uncommon. There are few data which specifically answer the question, but there is a suggestion that the syndromes associated with hormonal hypersecretion may be milder in this age group. Conventional treatment with drugs, surgery and radiotherapy should be decided on an individual basis as these therapies appear to be well tolerated and beneficial in selected patients.