Insulin resistance and advancing age: what role for dehydroepiandrosterone sulfate?

The Less We Eat, the Longer We Live: Can Caloric Restriction Help Us Become Centenarians?

Striving for longevity is neither a recent human desire nor a novel scientific field. The first article on this topic was published in 1838, when the average human life expectancy was approximately 40 years. Although nowadays people on average live almost as twice as long, we still (and perhaps more than ever) look for new ways to extend our lifespan. During this seemingly endless journey of discovering efficient methods to prolong life, humans were enthusiastic regarding several approaches, one of which is caloric restriction (CR). Where does CR, initially considered universally beneficial for extending both lifespan and health span, stand today? Does a lifelong decrease in food consumption represent one of the secrets of centenarians’ long and healthy life? Do we still believe that if we eat less, we will live longer? This review aims to summarize the current literature on CR as a potential life-prolonging intervention in humans and discusses metabolic pathways that underlie this effect.

Visceral adiposity index and DHEAS are useful markers of diabetes risk in women with polycystic ovary syndrome

OBJECTIVE

On the basis of the known diabetes risk in polycystic ovary syndrome (PCOS), recent guidelines of the Endocrine Society recommend the use of an oral glucose tolerance test (OGTT) to screen for impaired glucose tolerance (IGT) and type 2 diabetes (T2DM) in all women with PCOS. However, given the high prevalence of PCOS, OGTT would have a high cost-benefit ratio. In this study, we identified, through a receiver operating characteristic analysis, simple predictive markers of the composite endpoint (impaired fasting glucose (IFG) or IGT or IFG+IGT or T2DM) in women with PCOS according to the Rotterdam criteria.

DESIGN

We conducted a cross-sectional study of 241 women with PCOS in a university hospital setting.

METHODS

Clinical, anthropometric, and metabolic (including OGTT) parameters were evaluated. The homeostasis model assessment of insulin resistance (HOMA2-IR), the Matsuda index of insulin sensitivity, and the oral dispositional index and visceral adiposity index (VAI) were determined.

RESULTS

Out of 241 women included in this study, 28 (11.6%) had an IFG, 13 (5.4%) had IGT, four (1.7%) had IFG+IGT, and four (1.7%) had T2DM. Among the anthropometric variables examined, the VAI had a significantly higher C-statistic compared with BMI (0.760 (95% CI: 0.70-0.81) vs 0.613 (95% CI: 0.54-0.67); P=0.014) and waist circumference (0.760 (95% CI: 0.70-0.81) vs 0.619 (95% CI: 0.55-0.68); P=0.028). Among all the hormonal and metabolic serum variables examined, DHEAS showed the highest C-statistic (0.720 (95% CI: 0.65-0.77); P<0.001).

CONCLUSIONS

In addition to fasting glucose, the VAI and DHEAS may be considered useful tools for prescreening in all women with PCOS without the classical risk factors for diabetes.

Dehydroepiandrosterone sulfate and insulin resistance in patients with polycystic ovary syndrome

OBJECTIVE

To test the hypothesis that increasing DHEAS levels is associated with improved insulin resistance in patients with polycystic ovary syndrome (PCOS).

DESIGN

Cross-sectional cohort analysis.

SETTING

Academic medical center.

PATIENT(S)

Three hundred fifty-two women with PCOS.

INTERVENTION(S)

Patients presenting for evaluation of symptoms related to androgen excess were evaluated physically and biochemically through laboratory analysis.

MAIN OUTCOME MEASURE(S)

Circulating DHEAS, total T, free T, sex hormone-binding globulin (SHBG), and 17-hydroxyprogesterone (17-OHP) levels, and calculated homeostasis model assessment of insulin resistance (HOMA-IR).

RESULT(S)

Bivariate analysis indicated that all parameters were associated with HOMA-IR, except 17-OHP and age, and confirmed a negative correlation between DHEAS and HOMA-IR. Multivariate analysis indicated that increases in DHEAS, SHBG, 17-OHP, and age were associated with decreasing HOMA-IR, whereas increases in free T, body mass index (BMI), and waist-to-hip ratio (WHR) were associated with increasing HOMA-IR. In decreasing order of importance, the following variables predicted insulin resistance: BMI > WHR > age > DHEAS > free T > SHBG > 17-OHP.

CONCLUSION(S)

DHEAS is negatively correlated to insulin resistance in patients with PCOS, and in our model ranked just behind other well-established predictors including BMI, WHR, and age. Whether this is due to a direct beneficial effect on insulin action by adrenal androgens such as DHEA, or whether DHEAS simply reflects the circulating levels of hyperinsulinemia, remains to be determined.

Metabolic aspects of the extreme longevity

Starting from young to very old subjects, aging is associated with a progressive remodeling. Such an age-dependent remodeling process mainly affects anthropometrics, endocrine and thus, also metabolic factors. Interestingly, it occurs in some individuals successfully, while in others unsuccessfully. Centenarians in good health conditions are a very selected group of subjects representing an exceptional condition. Why the centenarians reach the extreme human life span is still unknown. Thus, in this article we will review the best known causes of age-related insulin resistance, outline the main metabolic differences between aged subjects and healthy centenarians, underline the clinical relevance of insulin resistance in the elderly and finally, we will try to propose a unifying hypothesis for explaining the development of insulin resistance with aging.

The Role of Dehydroepiandrosterone Levels on Physiologic Acclimatization to Chronic Mountaineering Activity

Previous studies have reported that glucose tolerance can be improved by short-term altitude living and activity. However, not all literature agrees that insulin sensitivity is increased at altitude. The present study investigated the effect of a 25-day mountaineering activity on glucose tolerance and its relation to serum levels of dehydroepiandrosterone-sulfate (DHEA-S) and tumor necrosis factor-alpha (TNF-alpha) in 12 male subjects. On day 3 at altitude, we found that serum DHEAS was reduced in the subjects with initially greater DHEA-S value, whereas the subjects with initially lower DHEA-S remained unchanged. To further elucidate the role of DHEA-S in acclimatization to mountaineering activity, all subjects were then divided into lower and upper halves according to their sea-level DHEA-S concentrations: low DHEA-S (n = 6) and high DHEA-S groups (n = 6). Glucose tolerance, insulin level, and the normal physiologic responses to altitude exposure, including hematocrit, hemoglobin, erythropoietin (EPO), and cortisol were measured. We found that glucose and insulin concentrations on an oral glucose tolerance test were significantly lowered by the mountaineering activity only in the high DHEA-S group. Similarly, hematocrit and hemoglobin concentration in altitude were increased only in the high DHEA-S group. In contrast, the low DHEA-S subjects exhibited an EPO value at sea level and altitude greater than the high DHEA-S group, suggesting an EPO resistance. The findings of the study imply that DHEA-S is essential for physiologic acclimatization to mountaineering challenge.

Association of decrease in serum dehydroepiandrosterone sulfate levels with the progression to type 2 diabetes in men of a Japanese population: the Funagata Study

Association of serum dehydroepiandrosterone sulfate (DHEAS) levels with insulin resistance and impairment of insulin secretion have been reported. We here examined the association of serum DHEAS levels with type 2 diabetes mellitus (DM) and the progression to DM. The serum DHEAS levels at baseline (from 1995 to 1997) were evaluated in 1709 individuals (998 women and 711 men) from a cohort population (n = 3706) of the Funagata Study. Glucose tolerance was evaluated at baseline as well as at 5-year follow-up examinations (n = 970, follow-up rate, 56.8%) according to the 1985 World Health Organization criteria. The statistical significance of the difference between any 2 groups was determined by the Student t test. Multiple logistic regression analysis determined the association of the traits with the progression to DM at the 5-year follow-up examinations. P < .05 was accepted as statistically significant. The serum DHEAS levels were significantly lower in DM than in normal glucose tolerance. However, this difference was not significant when adjusted for age. In men, the decrease in serum DHEAS levels by the 5-year follow-up examinations was significantly larger in the subjects who became diabetic than in the subjects who remained normal glucose tolerance, even when adjusted for age ( P = .0003). Multiple logistic regression analysis revealed a significant association of the decrease in serum DHEAS levels with the progression to DM, with an odds ratio (per 0.1 log ng/mL) of 1.410 (95% confidence interval [CI], 1.020-1.948, P = .038), independently from age, height, and 2-hour plasma glucose in men. A decrease in serum DHEAS levels seems to be associated with the progression to DM in Japanese men.

Effect of dehydroepiandrosterone replacement on insulin sensitivity and lipids in hypoadrenal women

DHEA (dehydroepiandrosterone) replacement is not part of the current standard of care in hypoadrenal subjects. Animal studies have shown that DHEA administration prevents diabetes. To determine the physiological effect of DHEA replacement on insulin sensitivity in adrenal-deficient women, we performed a single-center, randomized, double-blind, placebo-controlled, crossover study in 28 hypoadrenal women (mean age 50.2 +/- 2.87 years) who received a single 50-mg dose of DHEA daily or placebo. After 12 weeks, insulin sensitivity was assessed using a hyperinsulinemic-euglycemic clamp. DHEA replacement significantly increased DHEA-S (sulfated ester of DHEA), bioavailable testosterone, and androstenedione and reduced sex hormone-binding globulin levels. Fasting plasma insulin and glucagon were lower with DHEA (42 +/- 4.94 vs. 53 +/- 6.58 pmol/l [P = 0.005] and 178 +/- 11.32 vs. 195.04 +/- 15 pmol/l [P = 0.02], respectively). The average amount of glucose needed to maintain similar blood glucose levels while infusing the same insulin dosages was higher during DHEA administration (358 +/- 24.7 vs. 320 +/- 24.6 mg/min; P < 0.05), whereas endogenous glucose production was similar. DHEA also reduced total cholesterol (P < 0.005), triglycerides (P < 0.011), LDL cholesterol (P < 0.05), and HDL cholesterol (P < 0.005). In conclusion, replacement therapy with 50 mg of DHEA for 12 weeks significantly increased insulin sensitivity in hypoadrenal women, thereby suggesting that DHEA replacement could have a potential impact in preventing type 2 diabetes.

Vanadyl sulfate ameliorates insulin resistance and restores plasma dehydroepiandrosterone-sulfate levels in fructose-fed, insulin-resistant rats

OBJECTIVES

To elucidate whether vanadyl sulfate ameliorates the decreased dehydroepiandrosterone sulfate (DHEAS) in hyperinsulinemic rats, we evaluated plasma DHEAS, insulin and triglyceride (TG) levels in fructose-induced, insulin-resistant rats.

DESIGN AND METHODS

Animals were divided into three groups: control (C), fructose fed (F-F), and vanadyl-treated fructose fed (F-T). Control animals were fed with standard chow; F-F and F-T groups fed with 66% fructose diet. F-F and C groups received tap water; F-T group received water supplemented with 0.2 mg/ml vanadyl sulfate.

RESULTS

Fasting plasma glucose levels of three groups were comparable. Vanadyl treatment prevented the increase in plasma insulin and TG in the F-T group (P < 0.001) compared with the F-F group. Fructose feeding led to a decrease in plasma DHEAS in the F-F group (P < 0.001) compared with the C group. Vanadyl treatment prevented the decrease in plasma DHEAS in the F-T group (P < 0.001) compared with the F-F group.

CONCLUSIONS

Our results indicated that the hyperinsulinemia in fructose-fed, insulin-resistant rats is associated with low levels of DHEAS. Vanadyl sulfate probably restores plasma DHEAS, due to the improved insulin action.

Living longer--but better?

The highest attained age has increased by about 20 years since the beginning of the 19th century. In the course of the 1990s, more than ten individuals reached 115 years or more, including Jeanne Calment who attained the age of 122 years. In low-mortality countries, the number of centenarians has doubled every decade since 1950. This dramatic increase was mainly due to periodical effects related to the drastic fall in mortality among the elderly. The fact that centenarians are survivors does not mean that they are healthy. A high prevalence of comorbidity is found, and many centenarians have survived major diseases thanks to medical treatment and surgery. It is, however, possible that the comorbidity is less serious than in younger elderly. Certain personality traits may also be important in surviving health-threatening conditions. Furthermore, a number of biological and cognitive functions seem to be well-preserved in several centenarians. The influence of the apoE-gene and other genes involved in fundamental mechanisms illustrates that with advancing age and increasing mortality even small risks may have a substantial effect on survival to 100 years. A small proportion of long-livers may be considered as relatively autonomous, and this proportion will probably increase in the future. We are living longer and seem to postpone the terminal dependent phase to higher ages. Longevity may thus be perceived as part of our postmodern condition with its mix of pleasure and suffering.

Age-related insulin resistance: is it an obligatory finding? The lesson from healthy centenarians

It is widely known that advancing age is associated with impaired glucose handling. A unifying hypothesis explaining the relationship between aging and insulin resistance might encompass four main pathways, namely: (a) anthropometric changes (relative and absolute increase in body fat combined with a decline in fat free mass) which could be the anatomic substrate for explaining the reduction in active metabolic tissue; (b) environmental causes, mainly diet style and physical activity; (c) neuro-hormonal variations [decline in plasma dehydroepandrosterone sulphate (DHEAS) and IGF-1]; and finally (d) the rise in oxidative stress. Indeed previous studies have also investigated the occurrence and the degree of insulin resistance in healthy centenarians. Such data demonstrated that age-related insulin resistance is not an obligatory finding in the elderly and that healthy centenarians have a preserved insulin action compared to aged subjects. Why insulin action is preserved in centenarians is still not known. Nevertheless, a possible approach to the question is to outline the centenarians' anthropometric, endocrine and metabolic characteristics in order to design a clinical picture of such metabolic "successful aging". According to the remodeling theory of age, the preserved insulin action in centenarians might be the net result of the continuous adaptation of the body to the deleterious changes that occur over time. Nevertheless, only future longitudinal studies specifically designed to investigate the relationship between extreme old age and degree of insulin sensitivity will provide a conclusive answer with regard to the pathophysiology of adaptive metabolic changes occurring in the elderly.

Low dehydroepiandrosterone and ischemic heart disease in middle-aged men: prospective results from the Massachusetts Male Aging Study

The adrenal steroid dehydroepiandrosterone (DHEA) and its sulfate (DHEAS) have been characterized as "protective" against ischemic heart disease (IHD), especially in men, on the basis of sparse epidemiologic evidence. The authors used data from the Massachusetts Male Aging Study, a random sample prospective study of 1,709 men aged 40-70 years at baseline, to test whether serum levels of DHEA or DHEAS could predict incident IHD over a 9-year interval. At baseline (1987-1989) and follow-up (1995-1997), an interviewer-phlebotomist visited each subject in his home to obtain comprehensive health information, body measurements, and blood samples for hormone and lipid analysis. Incident IHD between baseline and follow-up was ascertained from hospital records and death registries, supplemented by self-report and evidence of medication. In the analysis sample of 1,167 men, those with serum DHEAS in the lowest quartile at baseline (<1.6 microg/ml) were significantly more likely to incur IHD by follow-up (adjusted odds ratio = 1.60, 95 percent confidence interval: 1.07, 2.39; p = 0.02), independently of a comprehensive set of known risk factors including age, obesity, diabetes, hypertension, smoking, serum lipids, alcohol intake, and physical activity. Low serum DHEA was similarly predictive. These results confirm prior evidence that low DHEA and DHEAS can predict IHD in men.

Metabolic age modelling: the lesson from centenarians

Evolutionary theories of ageing, and data emerging from cellular and molecular biology of ageing, suggested that animals and humans capable of reaching an age close to the extreme limit of the life span should be equipped with a very efficient network of anti-ageing mechanisms. Indeed several evidences have demonstrated that starting from young to very old subjects, ageing is associated with a progressive remodelling. Thus, a new paradigm, the remodelling theory of age, was proposed. This theory, focusing on the human immune system, suggested that immunosenescence is the net result of the continuous adaptation of the body to the deteriorative changes occurring over time. According to this hypothesis, body resources are continuously optimized, and immunosenescence must be considered a very dynamic process including both loss and gain. Whether the metabolic pathways and the endocrine functions are also part of the age remodelling is not investigated. The aim of this review is to focus on the age-related changes in metabolic pathways and endocrine functions and to demonstrate that healthy centenarians (HC) represent the best living example of successful age-remodelling in whom the age remodelling has occurred without problems. In order to design the clinical picture of such successful ageing, anthropometric, endocrine and metabolic characteristics of healthy centenarians (HC), compared with aged subject, have been outlined.

Predictors and clinical significance of declining plasma dehydroepiandrosterone sulfate in old age

Dehydroepiandrosterone sulfate (DHEAS) was measured in random persons of three age cohorts (75, 80 and 85 years, N=271) at five-year intervals in order to find out predictors and significance of declining DHEAS in old age. The mean values decreased from 2.88 micromol/L to 2.39 micromol/L in men (p<0.001), and from 1.93 micromol/L to 1.73 micromol/L in women (p<0.05) at entry. Strong correlations were found between the baseline levels of DHEAS and those measured after five years both in men (r=0.727, p<0.001) and women (r=0.605, p<0.001), and the changes in DHEAS were associated with DHEAS levels at entry (r=-0.418, p<0.05). Baseline DHEAS was higher (2.47 micromol/L vs 2.05 micromol/L, p<0.05) and the decline more pronounced (-0.50 micromol/L vs 0.20 micromol/L, p<0.05) in the healthy subjects than in those suffering from diseases at entry, but the percentage five-year decline was similar (-6.5% and -5.2%) in both groups. The five-year decline in DHEAS was predicted neither by the baseline levels of risk indicators, e.g., serum lipids, body mass index, electrocardiographic, nor echocardiographic findings at entry. The age-and gender-adjusted baseline levels of DHEAS predicted neither mortality nor cognitive decline with 5- and 10-year follow-up periods. The 5-year decline in DHEAS was significant (p<0.05) in the subjects who died or developed cognitive decline during the subsequent 5-year follow-up. However, the changes did not differ significantly from those with favorable prognosis. The data indicate that the decline in DHEAS is primarily a gender-specific aging phenomenon, and only partly a consequence of actual diseases and frailty.

Low plasma insulin-like growth factor-1 concentrations predict worsening of insulin-mediated glucose uptake in older people

OBJECTIVE

The relationship among insulin action, advancing age, and insulin like growth factor-1 (IGF-1) is poorly understood. To gain further insight, the predictive role that low plasma IGF-1 concentration may have on insulin- mediated glucose uptake in older persons was investigated.

DESIGN

The study was designed as a longitudinal, observational trial.

PARTICIPANTS

Fifty-eight healthy aged (73.1+/-9.4 years) subjects (31 males/27 females) were followed up for 12 months.

MEASUREMENTS

At baseline and at the end of the follow-up, insulin-mediated glucose uptake was assessed by euglycemic glucose clamp and plasma total IGF-1 and IGF-binding protein 3 (IGF-BP-3) in each subject, and concentrations were determined.

RESULTS

At baseline, plasma IGF-1 concentrations correlated with whole body glucose uptake (WBGD) (r = 0.39, P < .003), insulin-stimulated glucose oxidation (GOX) (r = 0.35, P < .009), and non-oxidative glucose metabolism (r = 0.37, P < .007). Such correlations were also independent of age, sex, body fat, and waist/hip ratio. Fasting plasma total IGF-1 concentrations (84+/-56 vs 63+/-44 microg/L, P < .040), plasma IGF-1/IGF-BP3 molar ratio (0.13+/-0.05 vs 0.10+/-0.03 P < .050), and WBGD (34.8+/-5.0 vs 23.1+/-4.6 micromol/kg x min, P < .010) were more elevated at baseline than at the end of the follow-up. Low baseline fasting plasma IGF-1 concentration (RR = 1.5, 95%CI = 1.3-1.7) and plasma IGF-1/IGFBP-3 molar ratio (RR = 1.4, 95% CI = 1.3-1.8) predicted a decline in WBGD. The predictive role of plasma IGF-1 on age-related decline in WBGD was independent of age, sex, body fat, waist/hip ratio, and degree of physical activity (model 1), or of fasting plasma free fatty acid and triglyceride concentrations, LDL/HDL ratio, and basal adjusted respiratory quotient (model 2). Finally, low plasma IGF-1 concentration predicts a decline in WBGD independent of body fat, free fatty acids, waist/hip ratio, and basal adjusted respiratory quotient (model 3).

CONCLUSION

Our study demonstrates that fasting plasma IGF-1 concentration may have a modulatory role on insulin action in older people. This finding might prompt an evaluation of the direct effect of IGF-1 administration on insulin sensitivity in older adults.

Advancing age and insulin resistance: new facts about an ancient history

The relationship between advancing age and insulin resistance is widely known, but the cause(s) of such association are less well understood. Age-related changes in anthropometric characteristics and environmental factors (changes in diet habits and decline in physical activity) have been hypothesized as being among the main causes. More recently, the role of plasma insulin-like growth factor I (IGF-I), dehydroepiandrosterone sulphate (DHEAS) and tumour necrosis factor alpha (TNF-alpha) concentrations as well as the degree of oxidative stress have also been evaluated. As far as the anthropometric changes are concerned, a decline in fat-free mass and a relative or absolute increase in fat mass are common findings in aged subjects. Such changes are combined with a decline in plasma DHEAS and IGF-I concentration and a rise in plasma TNF-alpha concentrations and oxidative stress, which, in turn, may interact with the anthropometric changes determining the worsening in insulin-mediated glucose uptake. Finally, age-related environmental factors (changes in diet quality and decline in the degree of physical activity) might be a common factor allowing anthropometric factors and age-related remodelling to accelerate their negative impact on insulin action.