Effect of age on glucose tolerance, insulin secretion, and in vivo insulin action

iGlarLixi versus premixed insulin initiation in adults with type 2 diabetes advancing from basal insulin therapy: The SoliComplex real-world study

AIM

To compare outcomes in adults with type 2 diabetes (T2D) suboptimally controlled with basal insulin who initiated treatment with iGlarLixi or premixed insulin.

METHODS

This retrospective real-world analysis was conducted using data from adults (age ≥ 18 years) with T2D in the US Optum Clinformatics database who had previously received basal insulin and newly initiated iGlarLixi or premixed insulin. Cohorts were propensity-score matched on baseline characteristics using a greedy nearest neighbour-matching algorithm, and outcomes were assessed at 12 months. Subgroup analyses were performed for those aged 65 years or older and those with a baseline HbA1c of 9% or higher. The primary endpoint was treatment persistence in the overall population. Secondary endpoints were treatment adherence, healthcare resource utilization (HRU), costs, hypoglycaemia events and change in HbA1c from baseline.

RESULTS

Each cohort comprised 834 participants. In the overall population, treatment persistence at 12 months was statistically significantly higher for iGlarLixi versus premixed insulin: 42.5% versus 39.1%; hazard ratio 0.88; 95% confidence interval 0.778-0.998; P = .0465. Adherence and HbA1c reduction were similar between groups, whereas hypoglycaemia events, HRU and costs were numerically lower for iGlarLixi. Outcomes in both the age 65 years or older subgroup and in those with an HbA1c of 9% or higher were consistent with those for the overall population.

CONCLUSIONS

In this observational study in people with T2D suboptimally controlled on basal insulin, once-daily iGlarLixi was an effective treatment alternative to premixed insulin with significantly higher treatment persistence, similar adherence and HbA1c reduction, and numerically lower hypoglycaemia events, HRU and costs, regardless of age or baseline HbA1c.

Aging: a portrait from gene expression profile in blood cells

The availability of reliable biomarkers of aging is important not only to monitor the effect of interventions and predict the timing of pathologies associated with aging but also to understand the mechanisms and devise appropriate countermeasures. Blood cells provide an easily available tissue and gene expression profiles from whole blood samples appear to mirror disease states and some aspects of the aging process itself. We report here a microarray analysis of whole blood samples from two cohorts of healthy adult and elderly subjects, aged 43±3 and 68±4 years, respectively, to monitor gene expression changes in the initial phase of the senescence process. A number of significant changes were found in the elderly compared to the adult group, including decreased levels of transcripts coding for components of the mitochondrial respiratory chain, which correlate with a parallel decline in the maximum rate of oxygen consumption (VO2_max), as monitored in the same subjects. In addition, blood cells show age-related changes in the expression of several markers of immunosenescence, inflammation and oxidative stress. These findings support the notion that the immune system has a major role in tissue homeostasis and repair, which appears to be impaired since early stages of the aging process.

Age-related changes in clinical parameters and their associations with common complex diseases

The aim of the present study was to clarify the age-related changes in 13 clinical parameters and their associations with common complex diseases. Study subjects comprised 6,027 community-dwelling individuals who were recruited to a population-based longitudinal genetic epidemiological study. Bonferroni's correction was applied to compensate for multiple comparisons of association and P<0.0011 was considered statistically significant. Body mass index and waist circumference increased with age up to ~50 years and decreased thereafter in men, whereas the two parameters increased linearly with age in women. The prevalence of obesity was highest (41.1%) in men aged 40-49 years, after which it decreased with age. The prevalence of obesity in women increased with age to ≤32.2% in those aged ≥70 years. Systolic and mean blood pressure (BP), as well as pulse pressure, increased linearly with age in all subjects, whereas diastolic BP increased with age up to ~60 years and subsequently decreased. The prevalence of hypertension increased with age to ≤69.9 or 68.5% at age ≥70 years in men and women, respectively. The fasting plasma glucose level, blood hemoglobin A1c content and the prevalence of type 2 diabetes mellitus increased gradually with age in men and women. The serum triglyceride concentration increased with age up to ~50 years and decreased thereafter in men, whereas it increased linearly with age in women. The prevalence of hypertriglyceridemia increased to a peak of 56.8% at age 50-59 years and subsequently decreased in men, whereas in women it increased with age to ≤34.9% at ≥70 years. The serum high-density lipoprotein (HDL)-cholesterol concentration increased with age up to ~50 years and decreased thereafter in women. The prevalence of hypo-HDL-cholesterolemia increased gradually with age in women. The serum concentration of low-density lipoprotein (LDL)-cholesterol increased with age up to ~50 years and subsequently declined in men, whereas it increased linearly with age in women. The prevalence of hyper-LDL-cholesterolemia increased with age to ≤53.4% at 50-59 years in men and ≤63.9% at 60-69 years in women and it decreased thereafter in the two genders. The serum creatinine concentration and the estimated glomerular filtration rate increased or decreased linearly with age, respectively. The prevalence of chronic kidney disease (CKD) increased with age to ≤45.1 or 39.6% at ≥70 years in men and women, respectively. Therefore, these results indicate that 13 clinical parameters, as well as the prevalence of obesity, hypertension, type 2 diabetes mellitus, dyslipidemia and CKD, were significantly associated with age. They may therefore prove informative for the prevention of these diseases and contribute to the achievement of a healthy long life and successful aging.

Postchallenge glucose rises with increasing age even when glucose tolerance is normal

AIMS

Ageing increases the likelihood of developing diabetes, with associated cardiovascular disease. In a cross-sectional study, we sought to determine whether age is associated with an increase in glucose concentrations 1 h after an oral glucose challenge (1-h OGTT), even when glucose tolerance is normal (NGT).

METHODS

Among subjects in the NHANES II database, 2591 subjects with NGT and documented 1-h OGTT glucose concentrations were studied. The relationship between age and 1-h OGTT glucose concentrations was assessed in a multivariable linear regression analysis.

RESULTS

In a multivariable linear regression analysis, each 10-year increase in age conferred an additional 0.20 mmol/l increase in the 1-h OGTT glucose (P < 0.0001). Moreover, an interaction between age and gender was found such that 1-h OGTT glucose concentrations rose more rapidly with increasing age in men than in women. The impact of age on 1-h OGTT glucose was independent of both fasting and 2-h OGTT glucose concentrations.

CONCLUSIONS

One-hour OGTT glucose concentrations rise significantly with age even in subjects with NGT. Further investigation is warranted to explore the pathophysiological significance of such age-related impairment of glucose handling, which might increase the risk of cardiovascular disease even when patients do not meet criteria for the diagnosis of diabetes or prediabetes.

Predictors of worsening insulin sensitivity in postmenopausal women

OBJECTIVE

The purpose of this study was to determine predictors of worsening insulin sensitivity in postmenopausal women.

STUDY DESIGN

Seventy-one nonobese postmenopausal women were assigned randomly to receive hormone replacement therapy (conjugated estrogens, 0.625 mg, plus medroxyprogesterone acetate, 2.5 mg) or placebo daily for 1 year (34 women received hormone replacement therapy, and 37 women received placebo). At baseline and 12 months, the women received a computed tomography scan at the L4-L5 vertebral disk space, a dual x-ray absorptiometry scan, a euglycemic hyperinsulinemic clamp to measure insulin sensitivity, and a lipid profile. Declining insulin sensitivity was defined as the largest quartile change in insulin sensitivity in the women who received the placebo (-1.42 mg/min/kg lean body mass).

RESULTS

By univariate analysis, we found that significant predictors of worsening insulin sensitivity were the use of hormone replacement therapy, baseline insulin sensitivity, a younger age, and <10 years since menopause. By logistic regression, we determined that hormone replacement therapy use and higher baseline insulin sensitivity were independent predictors of worsening insulin sensitivity.

CONCLUSION

The use of hormone replacement therapy and baseline insulin sensitivity are significant independent predictors of the development of worsening insulin sensitivity in postmenopausal women.

Use of the Gottingen Minipig as a Model of Diabetes, with Special Focus on Type 1 Diabetes Research

Animal models of type 1 diabetes remain essential tools for investigation of the etiology and pathogenesis of the disease and, importantly, for the development of effective new treatments. Although a range of well-characterized and widely used models of type 1 diabetes in rodents are currently available, large animal models are a valuable complement to rodent models for both physiological and practical reasons. The pig is very useful in many aspects as a model for human physiology and pathophysiology because many organ systems of this species, as well as physiological and pathophysiological responses, resemble those of the human. The Göttingen minipig is particularly suitable for long-term studies because of its inherent small size and ease of handling, even at full maturity. Of particular relevance to the field of type 1 diabetes are the many similarities evident between humans and pigs with regard to pharmacokinetics of compounds after subcutaneous administration, structure and function of the gastrointestinal tract, morphology of the pancreas, and the overall metabolic status of the two species. Because spontaneous type 1-like diabetes is very rare in pigs, a model of the condition must be induced experimentally, either surgically or chemically. This process is discussed, and the use of the pig as a model in islet transplantation and diabetic complications is briefly summarized.

Interaction between aging and syndrome X: new insights on the pathophysiology of fat distribution

Increased fat mass (FM), and in particular a specific increase in visceral fat (VF), may account for the age-associated decrease in insulin action and the development of Syndrome X. Utilizing chronic caloric restriction (CR) with aging in a rodent model, we dissociated the effects of VF and FM, and demonstrated that the decrease in VF accumulation was sufficient to prevent the marked decrease in hepatic insulin action. This suggests that the typical increase in VF with aging, rather than aging per se, determines hepatic insulin resistance. To directly assess the role of VF, we studied rats after surgical removal of VF or sham operation. Surgical extraction of VF (which accounts for approximately 10% of total fat) improved hepatic insulin action by more than twofold. We studied the role of fat-derived peptides in the regulation of body composition and insulin action. While VF extraction resulted in decreased gene expression for leptin and TNF-alpha in the subcutaneous adipose, administration of leptin selectively decreased visceral fat (approximately 60%), and enhanced the action of insulin on inhibiting hepatic glucose production (approximately 80%). Thus, the cause-effect relationship between the age-related increase in VF and the decrease in hepatic insulin action may involve the failure of leptin to "cross talk" with other fat depots to regulate fat distribution.

Age-related reduction in glucose elimination is accompanied by reduced glucose effectiveness and increased hepatic insulin extraction in man

This study examined whether insulin secretion, insulin sensitivity, glucose effectiveness (SG), and hepatic extraction (HE) of insulin are altered by age when glucose tolerance is normal. A frequently sampled i.v. glucose tolerance test was performed in 20 elderly (E, 10/10 male/female, all 63 yr old) and in 20 young subjects (Y, 10/10 male/female, all 27 yr old), who were similar in body mass index and 2-h blood glucose during oral glucose tolerance test. E exhibited impaired glucose elimination (i.v. tolerance index, 1.31 +/- 0.10 vs. 1.70 +/- 0.12% min-1; P = 0.019). First-phase insulin secretion and SI did not differ between the groups, whereas E had lower glucose sensitivity of second-phase insulin secretion (0.40 +/- 0.07 vs. 0.70 +/- 0.08 (pmol/L)min-2/(mmol/L), P = 0.026), lower SG, 0.017 +/- 0.002 vs. 0.025 +/- 0.002 min-1, P = 0.004), and higher HE (81.3 +/- 2.4 vs. 73.2 +/- 2.1%, P = 0.013). Across both groups, SG correlated positively with glucose tolerance index (r = 0.58, P < 0.001) and negatively with HE (r = -0.54, P < 0.001). Plasma leptin and glucagon did not change by age, whereas plasma pancreatic polypeptide (PP) was higher in E (122 +/- 18 vs. 66 +/- 6 pg/mL, P = 0.004). PP did not, however, correlate to any other parameter. We conclude that E subjects with normal oral glucose tolerance have reduced SG, impaired second-phase insulin secretion, and increased HE, whereas SI and first-phase insulin secretion seem normal. SG seems most related to age-dependent impairment of glucose elimination, whereas leptin, glucagon, and PP do not seem to contribute.

Insulin resistance shows selective metabolic and hormonal targets in the elderly

There has been no simultaneous evaluation of different aspects of insulin action in ageing. We studied 12 elderly (77 +/- 2 years) and 12 young (26 +/- 1 years) subjects with normal glucose tolerance and matched for sex, body mass index, lean body mass (LBM), blood pressure and physical activity, using a euglycaemic-hyperinsulinaemic clamp at about 350 pmol L-1 in combination with [3H]-glucose infusion. In the elderly group, hepatic glucose production was normal, fasting serum insulin and C-peptide were significantly increased (P = 0.001) and glucose utilization (34.4 +/- 2.4 vs. 44.4 +/- 3.2 mumol kg-1 LBM min-1, P = 0.02) and the percentage maximal suppression of C-peptide (58 +/- 6% vs. 79 +/- 5%, P = 0.02) during the clamp were reduced. Fasting plasma free fatty acid (FFA) and glycerol levels were similar in the two groups, but their percentage maximal suppression during the clamp was reduced in the elderly group (FFA 45 +/- 5% vs. 77 +/- 6%, P = 0.001; glycerol 43 +/- 5% vs. 76 +/- 3%, P = 0.001). Branched-chain amino acids (valine, leucine, isoleucine) and glucagon levels were similar in the two groups, both while fasting and during the clamp. Thus, insulin resistance in ageing appears selective on glucose utilization, inhibition of lipolysis and feedback inhibition of the B-cell secretion.

Insulin resistance in the elderly

The two-step hyperinsulinemic euglycemic clamp technique in young and aged adults demonstrated that insulin resistance observed in the elderly was due to a small reduction in pancreatic insulin output together with a small reduction in peripheral tissue response to insulin.

Peripheral and hepatic insulin sensitivity in healthy elderly human subjects

Insulin resistance has been reported in normal ageing but discrepancies between such studies may be related to compounding factors such as body composition and exercise patterns. We employed a two-step hyperinsulinaemic euglycaemic clamp to assess peripheral and hepatic tissue insulin sensitivity and glucose recycling in 13 elderly (E) and 14 young (Y) healthy subjects controlling for the above factors. There was no difference in basal hepatic glucose production (E: 2.36 +/- 0.06, Y: 2.47 +/- 0.1 mg kg-1 min-1; P = 0.4). At step 1 (insulin infusion 15 mU kg-1 h-1) glucose turnover was similar (E: 2.65 +/- 0.13, Y: 2.88 +/- 0.22 mg kg-1 min-1; P = 0.4) but hepatic glucose production was lower in the elderly group (0.20 +/- 0.16 vs 0.64 +/- 0.10 mg kg-1 min-1; P = 0.03). At step 2 (insulin infusion 50 mU kg-1 h-1) glucose turnover was similar (E: 7.60 +/- 0.24, Y: 8.05 +/- 0.34 mg kg-1 min-1; P = 0.3) and hepatic glucose production was equal but negative (E: -1.35 +/- 0.18, Y: -1.34 +/- 0.22 mg kg-1 min-1; P = 0.9). Glucose recycling did not differ between the groups at any stage. Similar serum insulin levels were achieved in both groups at each step. Decreased glucose tolerance was confirmed in E with a higher 2 h blood glucose after an OGTT (5.3 +/- 0.4 vs 4.1 +/- 0.3 mmol l-1; P = 0.03) but incremental insulin response was similar (E: 3236 +/- 289, Y: 3586 +/- 463 mU l-1 min-1; P = 0.5). We conclude that changes in hepatic tissue insulin sensitivity do not cause the deterioration in glucose tolerance observed with age. A small reduction in both peripheral tissue insulin sensitivity and late insulin secretion may be responsible.

Reduced beta-cell secretion and insulin hepatic extraction in healthy elderly subjects

One factor responsible for the altered carbohydrate metabolism in elderly subjects is impaired insulin release; however, difficulties in directly measuring insulin secretion have limited studies on pancreatic activity and on the contribution of the liver to insulin delivery. This study investigated beta-cell performance and insulin hepatic extraction under dynamic conditions in normal elderly subjects. Two strictly comparable groups of 12 young controls (Y, 27 +/- 1 (SE) years, 73 +/- 3 kg) and 12 elderly men (E, 69 +/- 2 years, 73 +/- 3 kg) were chosen on the basis of normal OGTT and normal insulin sensitivity in order to investigate a "pure" age effect. The subjects underwent a 4-hour frequently sampled intravenous glucose tolerance test (FSIGT) (dose 0.3 g/kg). Although no significant differences were found between the fasting levels of glucose and insulin (respectively: E: 89 +/- 3 mg/dL versus Y: 87 +/- 2, P greater than .1; and E: 5.0 +/- 0.5 microU/mL versus Y: 6.8 +/- 1.0, P greater than .05), basal C-peptide was found to be lower in the old subjects: 0.43 +/- 0.06 ng/mL versus 0.70 +/- 0.11 (P less than .025). The patterns of glucose and insulin during the FSIGT were similar, whereas C-peptide concentration in E was systematically lower, suggesting a reduced insulin secretion. To verify this hypothesis, we analyzed FSIGT data with a mathematical model-based method that provides a noninvasive direct measurement of the time courses of insulin secretion and hepatic extraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Age and glucose tolerance in healthy subjects

An important and still controversial issue is the role played by the aging process itself in the metabolic alterations observed in aged people. We previously reported that a group of normal elderly people exhibited glucose disposal comparable to that of young controls. In the present study we investigated the effect of age on beta-cell secretion, by analyzing C-peptide measurements. Ten elderly men (E, 70 +/- 2 years) with normal oral glucose test and ten young subjects (Y, 27 +/- 1 years) with matching ideal body weight formed the study group. They were studied under highly dynamic conditions by means of a 0.3 g/kg i.v. glucose tolerance test. Fasting glucose and insulin were not different in the two groups (Y: 87 +/- 2 mg/di, E: 88 +/- 3, p greater than 0.1; Y: 50 +/- 7 pM, E: 36 +/- 7, p greater than 0.05). Glucose-insulin data set was analyzed by means of the minimal model of glucose disappearance which provided two parameters for every individual, yielding a quantitative description of glucose utilization: i.e., SI, the index of insulin sensitivity, and SG, the fractional glucose disappearance at basal insulin (glucose effectiveness). Both parameters were unaltered by age (SI = Y: 6.30 +/- 0.41 10(-4)min-1/(microU/ml), E: 7.11 +/- 0.72, p greater than 0.1; SG = Y: 0.020 +/- 0.003 min-1, E: 0.019 +/- 0.002, p greater than 0.1). C-peptide time course in elderly people was systematically lower than in the control group (basal levels: Y: 252 +/- 36 pM, E: 129 +/- 17, p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Lymphocyte Na,K-ATPase is reduced in aged people

Na,K-ATPase-dependent 86Rb uptake, maximum velocity (Vmax), Michaelis constant (Km) of the uptake, and [3H]-ouabain binding were investigated in the lymphocytes of 10 elderly subjects (age greater than 60 years), and in 10 middle-aged (41 to 60 years) and 10 young controls (age less than or equal to 40 years). 86Rb uptake was reduced in elderly versus both middle-aged and young subjects (20.14 +/- 3.30 v 35.60 +/- 2.67, P = .002, and v 36.53 +/- 4.49 nmol, P = .012), as was the number of [3H]-ouabain binding sites per cell (32,662 +/- 2,215 v 40,420 +/- 1,184, P = .011, and v 40,596 +/- 1,349, P = .014). Vmax was reduced in elderly v young subjects (1.20 +/- 0.10 v 1.64 +/- 0.13, P = .034), but not versus the middle-age group (1.20 +/- 0.10 v 1.54 +/- 0.12 nmol.min-1, NS). Km was no different among the three groups. No differences were found between middle-aged and young subjects. Significant correlations were observed between age and Na,K-ATPase-dependent 86Rb uptake (r = -.620, P = .00009), Vmax (r = -.439, P = .024), and [3H]-ouabain binding sites (r = -.648, P = .002). Moreover, the site number was positively correlated with both uptake (r = .635, P = .002) and Vmax (r = .554, P = .011). These differences were observed both in women and men. We conclude that there is an age-dependent reduction in lymphocyte Na,K-ATPase activity, which is fully manifested over 60 years, and that this alteration is probably due to the reduced number of functional units of Na,K-ATPase in advancing age.

Effect of age on glucose tolerance and glucose uptake in healthy individuals

Plasma glucose and insulin responses and basal and insulin-stimulated glucose uptake were determined in 24 non-obese, healthy, physically active individuals, divided into two groups on the basis of age. The mean (+/- SEM) age of the younger group was 33 +/- 3 years, in contrast to an age of 64 +/- 2 years for the older group. Plasma glucose concentrations were significantly higher (two-way ANOVA, P less than .001) for three hours after a 75 g oral glucose challenge in the older group, as was the plasma insulin response (two-way ANOVA, P less than .001). Furthermore, there was a significant correlation between age and total plasma glucose (r = 0.63, P less than .001) and insulin (r = 0.44, P less than .01) during the glucose tolerance test. However, the magnitude of the decrease in glucose tolerance with age was relatively modest. For example, total plasma glucose response was only 11% higher in the older group, and the plasma glucose concentration 120 minutes after the oral glucose load only increased approximately 2 mg/dL per decade. Glucose uptake during euglycemic clamp studies was also reduced in the older group, and this was true if the clamps were performed at plasma insulin concentration of approximately 10 microU/mL (P less than .05) or 60 microU/mL (P less than .10). However the differences were relatively modest in magnitude, ie, 10-25%. The fact that the increase in glucose uptake when plasma insulin was raised six-fold was similar in both groups suggests that insulin sensitivity does not decline with age.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of habitual physical activity on age-related glucose intolerance

Plasma glucose and insulin responses to a standard oral glucose challenge and a mixed meal were determined for two groups of male volunteers (office workers and laborers) and a group of female housewives or office workers. Although glucose tolerance declined with age to a certain degree in all three groups, the age-related change varied as a function of both level of habitual physical activity and gender. Specifically, the decline in glucose tolerance was greatest in the male office workers and least in the females. The plasma insulin responses did not increase with age in any of the groups. These results suggest that glucose tolerance decreases with age because there is a decline in insulin action, which is not compensated for by an increase in insulin secretion. Insulin sensitivity appears to be enhanced in females as compared with males. Sensitivity is also enhanced in males habitually engaged in physical labor; thereby accounting for the age-related decline being greatest in the male office workers. Finally, the results showed that although the loss of glucose tolerance with age varied from group to group, the quantitative nature of the change was modest in all three groups. These data further emphasize that very little change in glucose tolerance is associated with aging in generally healthy, nonobese individuals.

Nocturnal regulation of free fatty acids in healthy young and elderly men

To determine the effects of age on nocturnal fuel regulation, we measured spontaneous plasma glucose and free fatty acid (FFA) levels as well as counterregulatory hormones in healthy young (n = 9, mean age 26 +/- 3 years) and old (n = 10, mean age 69 +/- 3 years) men from midnight to 8 AM. FFA levels rose from midnight (660 +/- 80 mEq/L for young subjects, 545 +/- 55 mEq/L for old) to a peak mean level of 866 +/- 110 mEq/L at 3 AM in young and 713 +/- 120 mEq/L at 1:30 AM in old (P less than .05). FFA levels declined thereafter for both groups. FFA levels were lower in older subjects (P less than .05) but integrated glucose (P less than .05) and insulin (P less than .05) levels were higher. FFA levels were inversely related to integrated insulin (r = -0.46, P less than .05) and glucose concentrations (r = -0.66, P less than .05). Integrated insulin levels were significantly higher in older subjects, which may explain the lower FFA levels as may lower growth hormone levels in the older subjects. While fasting glucose responsivity to endogenous insulin is impaired in healthy older men, the FFA response appears to be preserved.

Age-related changes in postprandial plasma glucose, insulin, and free fatty acid concentrations in nondiabetic individuals

Plasma glucose, insulin, and free fatty acid (FFA) concentrations were measured from 0800 to 1600 hours in 40 nondiabetic individuals, separated into younger (38 +/- 1.4 years) and older (64 +/- 1.5 years) age groups. Meals were served at 0800 (20% total daily calories) and 1200 h (40% of total daily calories), and blood drawn just before the 0800 hours meal and at hourly intervals thereafter until 1600 hours. Statistical evaluation of the results of these measurements indicated that day-long plasma glucose and insulin levels were higher in the older individuals. In contrast, the day-long FFA response was reduced in this age group. These data suggest that the ability of insulin to maintain normal plasma glucose levels deteriorates with age, whereas regulation of FFA levels does not.

Effect of age and environmental factors on glucose tolerance and insulin secretion in a worker population

The effect of age on glucose tolerance, as differentiated from the effects of obesity, work and leisure physical activity, family history of diabetes, and the use of drugs known to adversely affect glucose tolerance and/or insulin secretion, has been analyzed in 732 factory workers aged 22 to 73 years. Glucose tolerance, as evaluated by the plasma glucose response to 75 g of oral glucose deteriorated with age, associated with an increase in plasma insulin levels. However, the age-related decrease in glucose tolerance also correlated significantly with degree of obesity, leisure-time physical activity, and the use of potential diabetogenic drugs. Partial correlation coefficients were calculated to define the effect of age per se on glucose tolerance, controlling for the presence of these other age-related variables. When this was done, the degree of correlation between age and glucose tolerance was reduced, particularly in women, to where it became of marginal statistical significance. The effect of age on insulin response was affected to a greater degree by age-related variables, and was no longer statistically significant when these other factors were taken into consideration. These data suggest that the elevation in plasma glucose and insulin levels associated with age are to a certain extent due to age-related environmental factors, and the deterioration in glucose tolerance with age is relatively modest in magnitude in a generally healthy population.

Increased basal gluconeogenesis in the aged rat

Post-absorptive gluconeogenesis from lactate measured in vivo increases 3-fold in 24-month-old rats compared to 3-month-old animals. Fractional lactate turnover rates showed no significant differences between the two groups of animals. Lower plasma glucose concentrations and insulin-glucagon ratios may explain the increase in gluconeogenesis observed in aged rats.

Effect of habitual physical activity on regulation of insulin-stimulated glucose disposal in older males

The goal of this study was to evaluate the effect of differences in habitual level of physical activity on insulin action in healthy males between 60 and 75 years of age. The study population consisted of 20 non-obese individuals with normal glucose tolerance: 13 older subjects (68 +/- 4 years) not exercising regularly and 7 older subjects (66 +/- 3 years) who exercised regularly. Measurements were made of body mass index (BMI), percentage body fat by underwater weighing, maximal O2 consumption by bicycle ergometry (VO2max), and insulin-stimulated glucose disposal by the insulin clamp technique. The results demonstrated that insulin-stimulated glucose disposal was significantly increased (P less than 0.001) in the normal older subjects who exercised regularly. Furthermore, a direct relationship (r = 0.74, P less than 0.001) existed between maximal aerobic capacity and in vivo insulin action, which was independent of either BMI or percentage body fat. These data are consistent with the view that the extensive variation previously noted in in vivo insulin-stimulated glucose disposal of older subjects is related to differences in habitual physical activity.

Exercise for the elderly

Sedentary elders experience significant decline in physical ability, functional capacity, and sense of well-being with aging. Activity programs can have an impact on these losses but also carry significant risks for potential participants. Heterogeneity of the aging population requires individual assessments of their medical condition and exercise tolerance in determining the goals and conduct of an exercise program. Properly applied, such programs can significantly improve the quality of life for the elderly.

Insulin resistance in older rats

Insulin-stimulated glucose utilization was estimated in vivo in 1.5-, 4-, and 12-mo-old rats with an insulin suppression test wherein the height of the steady-state plasma glucose ( SSPG ) concentration, at similar steady-state plasma insulin levels, provides a direct reflection of the efficiency of insulin-stimulated glucose disposal. In parallel studies, the effect of age on in vitro insulin-stimulated glucose uptake was assessed in perfused hindlimb preparations. In addition, changes in the activity of enzymes that regulate muscle glycolysis, glycogenesis, and glycogenolysis were determined in isolated soleus muscle. The results indicated that rats got heavier as they became older, and changes in weight were associated with parallel increases in mean (+/- SE) SSPG concentrations as rats grew from 1.5 (56 +/- 3 mg/dl) to 4 (172 +/- 6 mg/dl) to 12 mo of age (194 +/- 8 mg/dl). The age-related decline in in vivo insulin action was associated with a reduction in insulin action on muscle, and maximal insulin-stimulated glucose uptake by perfused hindlimbs of 12-mo-old rats was approximately 50% of the value seen with perfused hindlimbs from 1.5-mo-old rats. Soleus muscle enzyme activity also varied with age, with significant increases in glycogen synthase and decreases in glycogen phosphorylase documented. Furthermore, muscle glycogen phosphorylase activity, which fell during an insulin infusion in 1.5-mo-old rats, did not change when 12-mo-old rats were infused at comparable insulin levels. Finally, glycogen content was significantly increased (P less than 0.01) in soleus muscle from 12-mo-old rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma glucose and insulin responses to oral glucose in nonobese subjects and patients with endogenous hypertriglyceridemia

Plasma glucose and insulin responses to a 50-gm oral glucose challenge were determined in 396 nonobese subjects: 220 patients with endogenous hypertriglyceridemia and 176 normal persons. These groups were further subdivided on the basis of relative body weight: 1.0-1.1 and 1.1-1.2. Patients with endogenous hypertriglyceridemia whose obesity index was between 1.0 and 1.1 had significantly increased plasma glucose (more than 25%, P less than 0.001) and insulin (more than 18%, P less than 0.01) responses. Similar findings were also observed in patients with endogenous hypertriglyceridemia whose index of obesity was between 1.1 and 1.2, ie, there was a 25% increase in the plasma glucose response (P less than 0.001) and a 37% increase in the plasma insulin response (P less than 0.001). Thus, endogenous hypertriglyceridemia can occur in nonobese individuals, and these patients have an increase in their plasma glucose and insulin responses when weight-matched with nonobese normal subjects.