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Biomedical subjects

D Elahi

Publications and source records attributed to D Elahi.

At least 37 records · Page 2Linked to original sources
PubMed1998

Insulinotropic hormone glucagon-like peptide-1-(7-37) appears not to augment insulin-mediated glucose uptake in young men during euglycemia.

Glucagon-like peptide-1 (GLP-1) is an intestinal insulinotropic hormone that augments insulin secretion in response to meals and lowers blood glucose levels in both type 1 and type 2 diabetic subjects. It has been proposed that a substantial component of the glucose-lowering effects of GLP-1 occurs via insulin-independent mechanisms. However, the interpretations of the studies have been controversial. This study was conducted to examine whether glucagon-like peptide (GLP-1) has an insulin-like effect during euglycemia. Nine young lean men (age, 25 +/- 1.4 yr; body mass index, 24.0 +/- 0.7 kg/m2) volunteered to participate in two euglycemic clamp studies (n = 18 clamps) for 120 min. The initial clamp was performed with a primed continuous infusion of GLP-1 at a final rate of 1.5 pmol/kg.min from 0-60 min. At 60 min, the GLP-1 infusion was terminated, and euglycemia was maintained from 60-120 min. After the GLP-1 study, each individual's plasma insulin level was measured. A second study was performed that was identical to the first, with the infusion of regular insulin in place of GLP-1. Insulin infusion rates were designed in each individual to simulate plasma insulin levels produced during the GLP-1 infusion. The rate of disappearance of glucose was calculated for each subject. Basal plasma insulin levels were similar between studies and averaged 49 +/- 5 pmol/L. Basal GLP-1 levels were also similar (6.0 +/- 1.0 pmol/L). In response to the GLP-1 infusion, although basal plasma glucose levels were clamped, significant increases in insulin occurred in all subjects (P < 0.001). With the nearly identical plasma insulin levels during the two studies (30-60 min levels: GLP-1 study, 151 +/- 48; insulin study, 146 +/- 31 pmol/L), the rate of disappearance of glucose progressively increased in response to both GLP-1 and insulin infusions, but was not significantly different between the studies. The design of the study necessitated conducting the GLP-1 study first, which may have been accompanied by a greater stress than the second study. We, therefore, measured cortisol levels. Basal cortisol (and ACTH) levels were not different. However, cortisol levels significantly increased during the GLP-1 infusions, and this was preceded by an increase in ACTH levels. Somatostatin levels were not different either basally or during the clamps. We conclude that in the euglycemic state, an acute infusion of GLP-1 does not have insulin-like effects in lean nondiabetic men. Intravenous administration of GLP-1 activates hypothalamic neuroendocrine neurons.

Adrenocorticotropic Hormone↗
PubMed1998

The effect of age and glycemic level on the response of the beta-cell to glucose-dependent insulinotropic polypeptide and peripheral tissue sensitivity to endogenously released insulin.

Normal aging is characterized by a progressive impairment in glucose tolerance. An important mechanism underlying the glucose intolerance of aging is an impairment in glucose-induced insulin release. These studies were conducted to determine whether the age-related impairment in insulin release was caused by a decreased beta-cell sensitivity to glucose-dependent insulinotropic polypeptide (GIP). Thirty-one Caucasian men were divided into four groups: two young groups (age range: 19-26 yr, n = 15) and two old groups (age range: 67-79 yr, n = 16). Each volunteer participated in three studies (n = 93 clamps). Hyperglycemic clamps were conducted at two doses [basal plasma glucose (G) + 5.4 mmol/L and G + 12.8 mmol/L] for 120 min. In the initial hyperglycemic clamp, only glucose was infused. In subsequent studies, GIP was infused at a final rate of 2 or 4 pmol/ kg(-1) x min(-1) from 60-120 min. Basal plasma insulin and GIP levels were similar in the young (41 +/- 6 and 51 +/- 6 pmol/L) and the old subjects (42 +/- 6 and 66 +/- 12 pmol/L) in all studies. First- and second-phase insulin responses were similar during the control study and during the first 60 min of each GIP infusion study in both groups. The 90-120 min GIP values were similar between groups and between hyperglycemic plateaus during the 2 and 4 pmol/kg(-1) x min(-1) GIP infusion (young: 342 +/- 28 and 601 +/- 44 pmol/L, old: 387 +/- 45 and 568 +/- 49 pmol/L). In response to the GIP infusions, significant increases in insulin occurred in young and old at both glucose levels (P < 0.01). The potentiation of the insulin response caused by GIP was greater in the young subjects than in the old, in the G + 5.4 mmol/L studies (P < 0.05). However, the insulin response to GIP was similar in both young and old during the G + 12.8 mmol/L clamps. The insulinotropic effect of the incretin was higher in the young and in the old, in the G + 12.8 mmol clamps, than in the G + 5.4 mmol/L clamps. We conclude that normal aging is characterized by a decreased beta-cell sensitivity to GIP during modest hyperglycemia, which may explain, in part, the age-related impairment in glucose-induced insulin release. We also find that the insulinotropic effect of GIP is increased with increasing levels of hyperglycemia.

Adult↗
PubMed1998

Physiological importance of first-phase insulin release in elderly patients with diabetes.

OBJECTIVE: To assess the physiological role of first-phase insulin release in obese elderly patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: Moderately obese elderly patients (n = 14, mean age 77 +/- 2 years, BMI 28.4 +/- 0.7 kg/m2) with type 2 diabetes underwent three 180-min hyperglycemic clamp studies. In the control study, glucose alone was infused. In the first-phase study, human insulin was infused for the first 4 min at 12 mU/m2 to mimic first-phase insulin release. In the first-phase enhanced study, insulin was infused for the first 4 min at 24 mU.m-2 .min-1. Tritiated glucose methodology was used in all studies to measure glucose production and disposal rates. RESULTS: Glucose values were similar in all studies. In the control study, first-phase insulin response was absent. The peak insulin response occurred at 4 min in the first-phase and first-phase enhanced studies, but insulin values were substantially higher in the latter study (528 +/- 40 vs. 340 +/- 24 pmol/l, P < 0.0001). Second-phase insulin responses were not different among the studies. Glucose production and disposal rates were not significantly different among the studies. CONCLUSIONS: While absent first-phase insulin secretion is a marker of abnormal pancreatic function in obese elderly patients with type 2 diabetes, it is not important in the regulation of hepatic glucose output or peripheral glucose disposal.

Aged↗
PubMed1997

Glucagon-like peptide-1 can reverse the age-related decline in glucose tolerance in rats.

Wistar rats develop glucose intolerance and have a diminished insulin response to glucose with age. The aim of this study was to investigate if these changes were reversible with glucagon-like peptide-1 (GLP-1), a peptide that we have previously shown could increase insulin mRNA and total insulin content in insulinoma cells. We infused 1.5 pmol/ kg-1.min-1 GLP-1 subcutaneously using ALZET microosmotic pumps into 22-mo-old Wistar rats for 48 h. Rat infused with either GLP-1 or saline were then subjected to an intraperitoneal glucose (1 g/kg body weight) tolerance test, 2 h after removing the pump. 15 min after the intraperitoneal glucose, GLP-1-treated animals had lower plasma glucose levels (9.04+/-0.92 mmol/liter, P < 0.01) than saline-treated animals (11.61+/-0.23 mmol/liter). At 30 min the plasma glucose was still lower in the GLP-1-treated animals (8.61+/-0.39 mmol/liter, P < 0.05) than saline-treated animals (10.36+/-0.43 mmol/liter). This decrease in glucose levels was reflected in the higher insulin levels attained in the GLP-1-treated animals (936+/-163 pmol/liter vs. 395+/-51 pmol/liter, GLP-1 vs. saline, respectively, P < 0.01), detected 15 min after glucose injection. GLP-1 treatment also increased pancreatic insulin, GLUT2, and glucokinase mRNA in the old rats. The effects of GLP-1 were abolished by simultaneous infusion of exendin [9-39], a specific antagonist of GLP-1. GLP-1 is therefore able to reverse some of the known defects that arise in the beta cell of the pancreas of Wistar rats, not only by increasing insulin secretion but also by inducing significant changes at the molecular level.

Aging↗
PubMed1997

Effects of hypertonicity on water intake in the elderly: an age-related failure.

Dehydration is a common clinical syndrome associated with many illnesses and treatments in the elderly. Prior studies have shown diminished sensation of thirst during water deprivation. It is currently unclear whether age-related decreases in thirst perception impair the defense against a hyperosmolar challenge. To examine the impact of water ingestion during hyperosmolality, young and old subjects were allowed free access to water during and after an intravenous infusion of 5% hypertonic saline. Cumulative water intake and serum osmolality were compared between seven healthy young (20-28 yrs) and seven healthy old (72-89 yrs) volunteers during and following a two hour hypertonic saline infusion at a rate of 0.06 mlxkg(-1) min(-1). Serum osmolality and water intake were markedly different between the two groups. In the old group, serum osmolality increased by 17 mosmol/kg above baseline despite free access to water. In contrast, serum osmolality increased to only 7 mosmol/kg above baseline in the young group and did not rise further. By ingesting water, the young were able to defend against an additional increase in serum osmolality. The young drank approximately twice that of the old during the infusion period. Healthy older individuals drink less than young despite a significantly increased serum osmolality. This hypodipsia in old individuals increases their susceptibility to hypertonicity.

Adult↗
PubMed1997

Increased disorderliness of basal insulin release, attenuated insulin secretory burst mass, and reduced ultradian rhythmicity of insulin secretion in older individuals.

Insulin is secreted in a pulsatile fashion. Rapid pulses are considered to be important for inhibiting hepatic glucose output, and ultradian pulses for stimulating peripheral glucose disposal. Aging is characterized by a progressive impairment in carbohydrate tolerance. We undertook the current studies to determine whether alterations in pulsatile insulin release accompany the age-related changes in carbohydrate metabolism. Healthy young (n = 8; body mass index, 21 +/- 1 kg/m2; age, 24 +/- 1 yr) and old (n = 9; body mass index, 24 +/- 1 kg/m2; age, 77 +/- 2 yr) volunteers underwent two studies. In the first study, insulin was sampled every 1 min for 150 min, and pulse analysis was conducted using a recently validated multiparameter deconvolution technique. In the second study, insulin was sampled every 10 min for 600 min, and insulin release was evaluated by Cluster analysis. In the 150-min studies, insulin secretory burst mass (P < 0.05) and amplitude (P < 0.01) were reduced in the elderly. In addition, approximate entropy, a measure of irregularity or disorderliness of insulin release, was increased in the aged (P < 0.01). In the 600-min studies, interpulse interval was greater in the aged (P < 0.05), and burst number was less (P < 0.05). We conclude that normal aging is characterized by more disorderly insulin release, a reduction in the amplitude and mass of rapid insulin pulses, and a decreased frequency of ultradian pulses. Whether these alterations in insulin pulsatility contribute directly to the age-related changes in carbohydrate metabolism will require further study.

Activity Cycles↗
PubMed1997

Metabolic correlates of obesity and radiographic features of knee osteoarthritis: data from the Baltimore Longitudinal Study of Aging.

OBJECTIVE: To examine the relationship between metabolic correlates of obesity and radiographic knee osteoarthritis (OA). METHODS: We included 464 Caucasian men and 275 Caucasian women aged 40 years and above who were participants in the Baltimore Longitudinal Study of Aging. Subjects had bilateral anteroposterior standing knee radiographs read for features of OA using Kellgren-Lawrence scales. Resting blood pressure, fasting lipids, 2 h oral glucose tolerance test, and anthropometric measurements were obtained at the same visit as the knee radiograph. Metabolic correlates of obesity were compared between subjects with Kellgren-Lawrence grade > or = 2 (definite knee OA) and grade 0 (normal radiograph) by sex. RESULTS: Both men and women with knee OA had higher unadjusted systolic blood pressure than those with normal knee radiographs; unadjusted measures of glucose metabolism and lipids did not vary by presence of knee OA in men or women. After adjustment for age and obesity, systolic blood pressure did not vary by presence of knee OA in men. While women with knee OA did have higher adjusted mean systolic blood pressure than women with normal radiographs (127 +/- 2.4 vs 120 +/- 2.2 mm Hg; p = 0.04), both values were within normal range. Unexpectedly, men with knee OA had lower adjusted mean 2 h glucose levels compared to men without OA (7.5 +/- 0.2 vs 8.4 +/- 0.2 mmol/l; p = 0.01). Other adjusted variables did not differ by presence of knee OA. CONCLUSION: These data do not support the hypothesis that metabolic correlates of obesity are independently associated with radiographic knee OA after adjustment for age and obesity.

Adult↗
PubMed1996

Insulin response during the oral glucose tolerance test: the role of age, sex, body fat and the pattern of fat distribution.

To clarify their primary roles on insulin response to oral glucose, age and sex differences in body composition should be taken into account. Oral glucose tolerance tests were performed on 472 men and 299 women of the Baltimore Longitudinal Study of Aging, ranging in age from 20 to 96 years. Subjects who were taking medications or had any diseases which could affect glucose tolerance were excluded. In addition to insulin and glucose values for the glucose tolerance test, we calculated body mass index (BMI), percentage body fat from skinfolds (% Body Fat), waist hip ratio (WHR), mean glucose level over the 2-hour test (GM), the basal insulin (IO), and the mean insulin response over the 2-hour test (IM). There was no significant sex difference in mean age, but men had significantly higher BMI (25.6 vs 24.0 kg/m2), WHR (0.93 vs 0.76), and GM (8.5 vs 7.7 mM), while % Body Fat was lower (25% vs 33%). Unadjusted IO and IM levels were significantly higher in men than in women (51 vs 44 and 303 vs 231 pM--antilogs of log-normalized values). Insulin levels, adjusted for differences in age, % Body Fat, WHR, and GM by analysis of covariance, however, showed no sex differences (49 vs 46 and 282 vs 257 pM). Adjusted insulin levels declined significantly with age; IM fell progressively from 323 pM in 20 to 39-year olds, 267 pM in 40 to 59-year, 253 pM in 60 to 79-year, and 228 pM in 80 to 96-year olds (p < 0.01). We conclude that the sex differences in insulin levels are explained by differences in body habitus and post-load glucose levels, but that insulin levels decline with age per se.

Adipose Tissue↗
PubMed1996

Atrial natriuretic peptide levels in the elderly: differentiating normal aging changes from disease.

BACKGROUND: Atrial natriuretic peptide (ANP) levels increase with advancing age and in patients with cardiac dysfunction. Previous studies have failed to differentiate the elevated ANP levels of normal aging from those of cardiac disease. METHODS: To differentiate the increased ANP levels seen in normal aging from that of disease, fasting supine ANP was measured in healthy young (n = 24), healthy old (n = 90), and clinically stable but cardiovascularly diseased old (n = 269) residents of a life care facility. ANP levels were correlated with physical exam findings, blood chemistries, measures of physical and cognitive function, and medications. RESULTS: ANP levels were almost fourfold higher in the healthy elderly than in the young (11.4 +/- 1.1 (SEM) vs 3 +/- 0.3 pmol/L, p < .01), and two-and-one-half times higher in the cardiovascular-diseased elderly than the healthy elderly (29 +/- 1.9 vs 11.4 +/- 1.1 pmol/L, p < .01). An ANP value of 21 pmol/L has a sensitivity of 83% and specificity of 52% in distinguishing those elders classified as healthy from those classified as having chronic cardiovascular disease. ANP levels had positive univariate correlation with age (even from 70 to 102 years) and systolic blood pressure. ANP rose progressively with increasing numbers of markers of cardiovascular comorbidity. ANP was higher in subjects with jugular venous pressure > 10 cm, presence of a third heart sound, peripheral edema, artificial cardiac pacemaker, atrial arrhythmias, and in those taking digoxin, diuretics, or nitrates. On multivariate analysis independent predictors of ANP levels were, in descending order, nitrates, age, diuretics, and atrial arrhythmias. CONCLUSION: These data suggest that ANP levels greater than 21 pmol/L are associated with cardiovascular comorbidity in a clinically stable elderly cohort.

Adult↗
PubMed1996

Resistive training increases insulin action in postmenopausal women.

BACKGROUND: This study examined the effects of 4 months of resistive training in postmenopausal women on glucose metabolism and peripheral tissue sensitivity to endogenously released insulin. METHODS: Thirteen moderately obese (30-49% body fat) postmenopausal women (50-65 years) participated in the study. The six more obese women were enrolled in the resistive training with weight loss (RT & WL) program, while the remainder participated in resistive training alone (RT). beta-cell sensitivity to glucose and peripheral tissue sensitivity to endogenously released insulin were examined during hyperglycemic clamps (7.9 mmol/L above basal) before and after the intervention(s). RESULTS: The RT program resulted in a significant improvement in upper and lower body strength (p < .01) in all subjects. Body weight, fat mass, and percent body fat decreased with RT & WL (p < .001), but did not change with RT alone. There was no change in fat-free mass or maximal oxygen consumption after the intervention(s). Insulin response during the last 20 min of the 2 hr hyperglycemic clamps (7.9 mmol/L above basal plasma glucose levels) decreased after the intervention(s) in the entire group by 29% (p < .01), but decreased more in the group that lost weight (43%, p < .05) than in women who remained weight stable (16%, p = .05). Glucose utilization did not change. CONCLUSION: RT alone, or in combination with WL, increases insulin action and reduces hyperinsulinemia in postmenopausal women. This suggests that RT has the potential to ameliorate and perhaps prevent the development of insulin resistance and may reduce the risk for glucose intolerance and non-insulin-dependent diabetes mellitus (NIDDM) in postmenopausal women.

Aged↗
PubMed1996

A cross-sectional study on body composition and energy expenditure in women athletes during aging.

The relationships between total and regional body composition, intra-abdominal adipose tissue (IAAT), resting metabolic rate (RMR), and substrate oxidation were examined in 43 highly trained women athletes and 14 sedentary women aged 18-69 yr. Athletes were divided into four groups (18-29, 30-39, 40-49, and 50-69 yr) and controls into two groups (18-29 and 40-50 yr). Maximal oxygen consumption declined with age (r = -0.52, P < 0.0005) in the athletes and was higher in all groups of athletes than in controls (P < 0.0001). No differences in percent fat and fat-free mass (FFM) were found between the youngest and oldest athletes. Although body mass index was < 25 kg/m2 in all subjects, percent body fat and total fat mass were higher in controls than in athletes for both young and older women (all P < 0.05). FFM was higher in young athletes than in young controls (P < 0.0001). Despite similar percent fat among athletes, IAAT increased with age (r = 0.75, P < 0.0001), but subcutaneous abdominal fat and sagittal diameter did not. IAAT and subcutaneous abdominal fat were also higher in young controls than in young athletes and in older controls than in older athletes (all P < 0.005). Age and FFM were independent predictors of the decline in RMR in the athletes. Fat oxidation (g/day) was highest in the youngest athletes and declined with age (r = -0.47, P < 0.005). We conclude that intense chronic exercise in women athletes prevented the decline in FFM with age. Endurance-trained women have low IAAT stores, which may potentially reduce subsequent risk associated with the metabolic syndrome.

Adipose Tissue↗
PubMed1996

Pancreatic polypeptide administration improves abnormal glucose metabolism in patients with chronic pancreatitis.

Chronic pancreatitis (CP) is associated with lowered plasma levels and a blunted nutrient-induced release of pancreatic polypeptide (PP). To investigate the possible role of PP on glucose metabolism, we studied male patients with documented CP (n = 5) and obesity-matched control subjects (NL) (n = 6). Hepatic glucose production (HGP) and overall glucose disposal rates were determined by [3-3H]glucose infusion during a hyperinsulinemic-euglycemic clamp during three separate admissions. Basal rates of HGP were higher in CP patients. In response to an infusion of insulin (60 pmol.m-2.min-1), HGP fell 91 +/- 5% in NL subjects but only 68 +/- 8% in CP subjects (P < 0.05). One month later, the clamp was repeated during the final 2 h of an 8-h infusion of bovine PP (2 pmol.kg-1.min-1). HGP before the insulin infusion and its subsequent suppression (NL: 83 +/- 5%; CP: 86 +/- 15%) were nearly identical between groups. In follow-up studies 1 month after the PP infusion, HGP both basally and in response to insulin alone were similar to the first study. During oral glucose tolerance tests (OGTT) performed 18 h after the PP infusion, subjects with normal (n = 7) baseline OGTT responses showed no effect. All patients with diabetic (n = 3) or nondiagnostic (n = 1) OGTT responses, however, demonstrated lowered mean plasma glucose levels (approximately -2.3 mmol/L; range: -0.6 to -7.2 mmol/L). OGTTs repeated 1 month after the PP treatment showed a return to pretreatment responses. We conclude that chronic pancreatitis accompanied by PP deficiency is associated with partial hepatic resistance both in the basal state and in response to hyperinsulinemia. This impairment is reversed after iv PP administration. PP deficiency may therefore play a role in the development of pancreatogenic diabetes caused by pancreatic injury.

Adult↗
PubMed1996

The effects of acute hyperglycemia and hyperinsulinemia on plasma leptin levels: its relationships with body fat, visceral adiposity, and age in women.

The acute effects of hyperglycemia and hyperinsulinemia on plasma leptin levels were determined in 42 highly trained women athletes (18-69 yr) and 14 sedentary control women (18-50 yr, body mass index < 25 kg/m2), using the glucose clamp technique. The relationships of body composition, physical fitness, age, and plasma leptin levels were examined in all participants. In addition, the effect of weight loss and aerobic exercise and plasma leptin levels were examined in 4 Newly diagnosed untreated noninsulin-dependent diabetes mellitus patients. The time course of plasma leptin levels changed little from basal during hyperglycemic (approximately 10 mmol/L) or hyperinsulinemic-euglycemic (400-3000 pmol/L) clamp studies in either athletes, controls, or noninsulin-dependent diabetes mellitus patients. A strong correlation between plasma leptin levels and fasting insulin was present (r = 0.60, P < 0.001). Plasma leptin and percent fat were higher in controls than athletes (12.6 vs. 4.0 ng/mL and 33.2 vs. 20.8%; both P < 0.001). The relationships between percent fat (dual-energy x-ray absorptiometry) or intraabdominal adipose tissue (computed tomography) and leptin for the entire group were highly significant (r = 0.70, r = 0.52; P < 0.001). When percent fat was controlled, the relationship between fasting insulin and leptin remained (P < 0.002). There was not a significant association between age and plasma leptin levels in a univariate analysis in this population. However, after adjustment for percent fat, a significant inverse relationship between age and leptin appeared (P < 0.05). The weight loss and aerobic exercise program resulted in an average 6 +/- 0.8 kg wt loss. Leptin levels decreased > 28% in each patient (P < 0.01). In conclusion, neither acute hyperglycemia or hyperinsulinemia affects plasma leptin levels. Percent fat is the strongest predictor of leptin levels, even in lean, highly trained women athletes.

Adipose Tissue↗
PubMed1996

In praise of the hyperglycemic clamp. A method for assessment of beta-cell sensitivity and insulin resistance.

The most widely used methods for the assessment of beta-cell response and peripheral tissue sensitivity to insulin include the oral glucose tolerance test (OGTT), the frequently sampled intravenous glucose tolerance test, and the hyperinsulinemiceuglycemic clamp technique. During an OGTT, glucose levels increase after a variable lag period, then reach a peak and fall variably among individuals. The response even varies in the same subject upon repeat testing. A more reproducible glucose curve is achieved with an intravenous glucose tolerance test in which the plasma glucose levels rise rapidly to a very high level and fall exponentially. In neither of the two methods is a steady-state glucose level achieved. In the hyperinsulinemic-euglycemic clamp technique, a steady-state glucose level can be maintained at any level of hyperinsulinemia. However, an assessment of beta-cell sensitivity is not obtained. The less used hyperglycemic clamp technique can assess beta-cell sensitivity as well as peripheral tissue sensitivity. Moreover, a measure of glucose effectiveness or non-insulin-mediated glucose uptake can also be determined. With this technique the beta-cells of all subjects are stimulated with the same arterial glucose concentration, thus enabling assessment of beta-cell response to identical plasma glucose levels. Comparison of responses to stable hyperglycemic stimuli can be made in glucose-tolerant and -intolerant states with the addition of various substances, either alone or in combination. The use of the hyperglycemic clamp and several of its variant forms is reviewed as an alternative method for assessment of glucose homeostasis.

Adult↗
PubMed1996

The effect of age on insulin resistance and secretion: a review.

Aging is associated with an increased incidence of hypertension, noninsulin-dependent diabetes mellitus, and coronary heart disease. Because these conditions often cluster in the same individuals, there has been speculation that a common mechanism is responsible for all of these pathological states. Both epidemiological and clinical research has shown that insulin resistance and/or hyperinsulinemia are associated with glucose intolerance, dyslipidemia (high plasma triglyceride and low high-density lipoprotein-cholesterol levels), and higher systolic and diastolic blood pressures. Therefore, insulin resistance and hyperinsulinemia have been proposed as the causal link among the elements of the cluster mentioned above, now most commonly referred to as the insulin resistance syndrome, syndrome X, or the metabolic syndrome. The elderly are more glucose intolerant and insulin-resistant, but it remains controversial whether this decrease in function is an inevitable consequence of "biological aging" or the result of what might be referred to as environmental or lifestyle variables: increased obesity, a detrimental pattern of fat distribution, or physical inactivity that usually accompany age. All of these modifiable environmental factors have also been shown to result in increases in insulin resistance and hyperinsulinemia and are risk factors for the development of the diseases of the metabolic syndrome. Recent interventional studies that have attempted to reverse these conditions in the elderly have shown improved insulin sensitivity, and glucose tolerance. Insulin secretion, on the other hand, seems to decrease with age even after adjustments for differences in adiposity, fat distribution, and physical activity. This may be responsible for the glucose intolerance in the very old even after improvements have been made in their lifestyle variables.

Aging↗
PubMed1995

Long-term effects of a high-carbohydrate diet and exercise on insulin action in older subjects with impaired glucose tolerance.

Carbohydrate metabolism was assessed in 20 glucose-intolerant subjects before and after 12 wk on a high-carbohydrate diet (HC) or the diet combined with exercise training (HC-EX). The diet provided 60% of energy as carbohydrate and 20% as fat. Neither treatment altered fasting glucose or insulin concentrations or their response to a meal. During a glucose clamp (216 pmol insulin/L) glucose disposal increased from 13.2 +/- 0.83 to 14.6 +/- 0.83 mumol.kg fat-free mass-1.min-1 (P < 0.05) in both groups. During more pronounced hyperinsulinemia (654 pmol/L) glucose disposal did not change significantly (49.9 +/- 3.8 to 50.7 +/- 3.8 mumol.kg fat-free mass-1.min-1). Muscle glycogen increased in the HC-EX group (78.5 +/- 8.1 to 161.1 +/- 15.7 mmol glucose/kg muscle), with no changes in the HC group. These results do not support the recommendation to increase the dietary carbohydrate content for improving postprandial glucose metabolism or insulin action in glucose-intolerant adults unless combined with exercise training, which promotes muscle glycogen storage.

Aged↗