Biomedical subjects

J D Tobin

Publications and source records attributed to J D Tobin.

At least 55 records · Page 3Linked to original sources

PubMed1990

The role of muscle loss in the age-related decline of grip strength: cross-sectional and longitudinal perspectives.

The decline of strength with age has often been attributed to declining muscle mass in older subjects. To investigate factors which might influence changes in strength across the life span, grip strength and muscle mass (as estimated by creatinine excretion and forearm circumference) were measured in 847 healthy volunteers, aged 20-100 years, from the Baltimore Longitudinal Study of Aging. Cross-sectional and longitudinal results concur that grip strength increases into the thirties and declines at an accelerating rate after age 40. However, the grip strength of 48% of subjects less than 40 years old, 29% of individuals 40-59 years old, and 15% of subjects older than 60 did not decline during the average 9-year follow-up. Grip strength is strongly correlated with muscle mass (r = .60, p less than .0001). However, using multiple regression analysis, grip strength is more strongly correlated with age (partial r2 = .38) than muscle mass (partial r2 = .16). Additionally, a residuals analysis demonstrates that younger subjects are stronger and older subjects are weaker than one would predict based on their muscular size. Thus, while strength losses are partially explained by declining muscle mass, there remain other yet undetermined factors beyond declining muscle mass to explain some of the loss of strength seen with aging.

Adult↗

PubMed1990

The age-associated decline in glomerular filtration in healthy normotensive volunteers. Lack of relationship to cardiovascular performance.

Whether the well-documented age-associated decline in the glomerular filtration rate, manifest as a decline in creatinine clearance, is secondary to an age-related change in cardiovascular performance is at present unknown. To answer this question, we measured arterial blood pressure, 24-hour creatinine clearance, and cardiac output determined from gated cardiac blood pool scans in the sitting position in healthy normotensive men (n = 75) and women (n = 42) (ages 25 to 82 years), from the Baltimore Longitudinal Study on Aging. These subjects were selected for the absence of cardiovascular disease, renal disease, and confounding medications. By linear regression analysis, creatinine clearance, expressed in mL/min/m2, declined cross-sectionally with age (creatinine clearance = 90 -0.33[age], r = .31, P less than .001), whereas systolic blood pressure in mm Hg increased with age (systolic blood pressure = 111 + 0.27[age], r = .30, P less than .001); cardiac output in L/min/m2 did not vary with age (r = .03, P = .74). In stepwise multiple regression analysis with age, cardiac index, and systolic blood pressure as independent variables and creatinine clearance as the dependent variable, only age was a significant predictor of creatinine clearance. (F = 11.31, DF + 116, r = .30, P less than .001). Thus, the age-associated decline in creatinine clearance is not modulated by changes in cardiac index or systolic blood pressure in healthy normotensive subjects.

Adult↗

PubMed1990

Vitamin D status and related parameters in a healthy population: the effects of age, sex, and season.

The effects of age, sex, renal function, and seasonal variation on serum parameters within the vitamin D endocrine system were studied cross-sectionally in a healthy population of 167 men and 114 women, aged 20-94 yr. Serum 25-hydroxy- and 1,25-dihydroxyvitamin D [25OHD and 1,25-(OH)2D] did not decline with age in either sex. Nonlinear regression using a sine function showed a significant seasonal variation in 25OHD and 1,25-(OH)2D in both sexes (P less than 0.005). Serum intact PTH increased significantly by 35% over the age span in both sexes (P less than 0.005). In women, serum phosphorus and total and ionized calcium remained constant with age. In sharp contrast, males had a marked 25% fall in phosphorus across the age span (r = -0.564; P less than 0.0001) and a slight but significant 4% decline in total and ionized calcium. Creatinine clearance declined markedly with age, but was not related to 1,25-(OH)2D in either sex. Only in men was there a significant but modest inverse relationship between creatinine clearance and PTH (r = -0.212; P less than 0.05), which was multicollinear with age. We conclude that in healthy individuals 1) compromised vitamin D status or serum 1,25-(OH)2D levels are not a normal concomitant of aging; 2) declining glomerular filtration does not appear to be the principle cause of the age-related rise in PTH; and 3) there are marked male-female differences in phosphorus metabolism across the age span.

Aging↗

PubMed1989

New radiographic grading scales for osteoarthritis of the hand. Reliability for determining prevalence and progression.

We developed and evaluated scales for grading the prevalence and progression of the individual radiographic features of osteoarthritis (OA) of the hand. Four equally time-spaced hand radiographs from 50 participants in the Baltimore Longitudinal Study of Aging, who were followed for at least 20 years, were read separately and "blindly" by 4 experienced, trained readers. Eleven hand joints were individually assessed for the presence of osteophytes, joint space narrowing, subchondral cysts, subchondral sclerosis, lateral deformity, and cortical collapse, and were also graded using the Kellgren/Lawrence scale, a global estimate of OA. The intraclass correlation coefficient was used to determine cross-sectional inter- and intrareader reliability. Interreader agreement on OA progression was evaluated using life-table analysis. Each of the grading scales for the individual radiographic features of OA of the hand, except for cysts, were cross-sectionally reliable between readers. Each reader was able to reproduce his original scores almost perfectly when grading the radiographs a second time. Using these scales, the different readers agreed on all the features of longitudinal progression of OA of the hand, except cysts. We believe that this method for grading hand radiographs for OA has proved to be reliable for both cross-sectional and longitudinal studies.

Adult↗

PubMed1989

Ovariectomy, dietary zinc, and bone metabolism in retired breeder rats.

Bone mineral turnover was studied in sham and ovariectomized (ovax) retired breeder rats after 16 wk of dietary treatment. Rats were fed either a commercial rat diet (CRD) containing high calcium and cholecalciferol or egg-white diets (EWD) containing 2 g Ca/kg, 1,25-(OH)2cholecalciferol (5 micrograms/kg), and either 10 or 200 mg zinc/kg. In rats fed EWD, high Zn enhanced femoral Zn deposition and concentration but did not affect serum Ca levels, bone mineral content (BMC), or turnover. Serum Ca levels and BMC were greater in sham rats and there was a gain in femoral Ca and phosphorus compared with the loss of these minerals in ovax rats. In CRD-fed ovax rats, values for these variables were similar to those of CRD-fed shams and there was no bone mineral loss. These data suggest that ovarian function may be a prerequisite for the beneficial effects of diets containing 1,25-(OH)2cholecalciferol and low Ca on bone metabolism.

Animals↗

PubMed1989

Studies in the distribution of body fat: I. Effects of age, sex, and obesity.

The pattern of body fat distribution has been shown to be related to a large number of variables of clinical importance. A variety of indices have been devised, many of them simple enough to be useful in large-scale clinical studies. Relationships among these several indices and systematic information on the effects of age, sex, and obesity have, however, not been systematically studied. Five anthropometric ratios that classify individuals into different body types have been computed for 1179 men and women aged 17-96 years. These are: waist hip ratio, arm thigh ratio, waist thigh ratio, waist arm ratio, and subscapular triceps skinfold ratio. In general, the age patterns show progressive trends toward increasing upper and central body fat deposition with age. In women there tends to be a postmenopausal acceleration of this trend. The ratios are distinctly higher in men than in women and are also independently influenced by the body mass index. Predictive equations that take age and BMI into account for each of the indices for men and women have been provided.

Adipose Tissue↗

PubMed1989

Studies in the distribution of body fat. II. Longitudinal effects of change in weight.

Information on the effects of age, sex, obesity and weight change on the fat distribution pattern has not been systematically reported. As an index of body fat distribution, the waist hip circumference ratio (WHR) was computed in 370 men and 177 women aged 22-86 years, participants of the Baltimore Longitudinal Study of Aging. For cross-sectional analysis, initial data on the participants were analyzed; for longitudinal study, the changes in the measurements related to weight change during a 5-year follow-up were analyzed. From cross-sectional analysis: (1) waist circumference is larger in men than in women and increases progressively with age; (2) hip circumference shows no consistent age or sex differences; (3) thus, the well known sex differences in WHR are totally attributable to differences in waist circumference; (4) increases in WHR with age occur in both men and women. From longitudinal analysis of weight change: (1) changes in waist and hip circumferences are correlated directly with changes in weight in both sexes, but there are large differential sex effects; (2) in men, waist changes dominate; (3) in women, waist and hip changes are nearly the same; (4) thus, weight changes in men have large effects on the WHR, while in women changes in WHR are very small. Men, as a group, have a more dangerous fat distribution pattern than women, but men as a group will show a more beneficial pattern of change in WHR with weight control than women.

Adipose Tissue↗

PubMed1988

Fiber intake, age, and other coronary risk factors in men of the Baltimore Longitudinal Study (1959-1975).

Fiber intake was estimated by 7-day diet record in community-dwelling men of the Baltimore Longitudinal Study of Aging. The mean intake of 845 men (age 20-103) was 3.82 +/- 0.03 g crude fiber/day which corresponds to approximately 15 g/day of dietary fiber. Fiber intake increased across the age span (slope = +0.022 +/- 0.003 g/yr, p less than .01). Longitudinal analysis of 380 men, each of whom provided 3-8 diet records over an average period of 8 yr, indicated that the increase in fiber intake occurred in each age group and was not the result of differential survival. Fiber intake was negatively correlated with body mass index. After clinical screening to eliminate variables which could independently influence coronary risk factors, multiple regression analyses including age and body mass index were conducted to examine the effect of fiber (adjusted for total calorie intake) on blood pressure, blood lipids, and glucose tolerance. For systolic and diastolic blood pressure, triglyceride, and fasting plasma glucose, higher fiber intake was associated with lower levels of the risk factors (p less than .05).

Adult↗

PubMed1987

Hypertension and the kidney.

The purpose of this study was to confirm, using longitudinal observations in a normal population, that the rate of decline in renal function (creatinine clearance) is inversely correlated with blood pressure. The negative regression coefficients plotting individual rates of decline over time (Bcr) against mean blood pressures (MBP) were highly significant (p less than 0.001) for all subjects and subjects in category 3 (normals). Although the Bcr also decreases significantly with age and MBP increases with age suggesting this might be an age effect, a multiple regression analysis shows that both MBP and age as independent variables exert statistically significant effects on Bcr, the dependent variable.

Adult↗

PubMed1986

Longitudinal study of bone loss in the second metacarpal.

This longitudinal study was undertaken to ascertain the rate of bone loss and to identify aging, cohort and/or time effects on bone loss in male participants of the Baltimore Longitudinal Study of Aging. Hand-wrist radiographs were obtained from 1958-1981 and were evaluated for total width, medullary width, and length of the second metacarpal. Data were analyzed using an age-time matrix with 8-year intervals for three epochs and nine age groups. The bone measurements were analyzed in three perspectives (cross-sectional, longitudinal and time-series). The results demonstrate that there is both a cross-sectional and longitudinal loss of cortical bone with age in the second metacarpal. Furthermore, the results show that males lose approximately 14% of their cortical bone, at a rate of about 2% per decade, over the adult lifespan. The majority of this loss occurs between the ages of 45 and 69 and is due primarily to aging and is not an artifact of cohort differences or secular change.

Adult↗

PubMed1986

Factors affecting attrition in the Baltimore Longitudinal Study of Aging.

In a longitudinal study of aging, the influence on attrition of age, marital status, education, occupation, distance between a subject's residence and study center, self-health and financial assessment, and method of recruitment was examined. Prospective, follow-up information on the subsequent active/dropout and alive/dead status on the 1088 subjects, who joined the Baltimore Longitudinal Study of Aging during the first twenty years (1958-1977), were studied using a proportional hazards model. Three analyses, each controlling for death in a different manner, produced similar results. The analysis indicates that age, education and distance have the strongest association with attrition (p less than 0.001), while self-health assessment has a lesser association (p less than 0.05). The lowest risk in age, for example, occurs in 40-49.9 year olds with subjects less than 30 having an increased risk of 91% and subjects 70 or older having an increased risk of 189%. Examination of attrition probabilities show that subjects living 500 or more miles from study center, ages 70 and older, with less than bachelors degree, and perceiving their health as average or below have the greatest probability of dropping out-approximately 3-fold greater than the average subject's probability.

Adolescent↗

PubMed1986

A longitudinal study of cognitive performance in noninsulin dependent (type II) diabetic men.

Diabetic men (noninsulin dependent, Type II) in the Baltimore Longitudinal Study of Aging were compared with nondiabetics on two cognitive performance tests--the Benton Visual Retention Test, a measure of nonverbal memory, and the Vocabulary subtest of the Wechsler Adult Intelligence Scale. Cross-sectional comparisons of 52 diabetics with matched controls and with 610 controls (covaried for age and education) found no group differences and no support for an accelerated cognitive aging effect of diabetes. In addition, longitudinal comparisons over six years and over twelve years found no effect of diabetes on change in cognitive performance. Possible reasons for disagreements of cross-sectional findings in the literature are discussed. One possibility is that only specific aspects of cognitive performance are adversely affected by diabetes. It is also possible that lower socio-economic status (as indexed by education) may be a risk factor in the effect of diabetes on cognitive performance, perhaps by delaying diagnosis and treatment.

Adult↗

PubMed1985

The effect of age and glucose concentration on insulin secretion by the isolated perfused rat pancreas.

Age changes in the beta-cell's sensitivity to glucose as well as in its overall capacity to secrete insulin may play a part in the glucose intolerance of aging. The isolated perfused rat pancreas preparation was used to study the effect of age and glucose level on insulin secretion. Overnight-fasted male Wistar 12- and 23-month-old rats had basal plasma glucose levels of 106 +/- 4 (SE) and 100 +/- 4 mg/dl. Perfusate glucose levels were raised from 80 mg/dl to either 150, 220, or 360 mg/dl for 50 min (n = 6 to 8 in each group). Insulin secretion followed the typical biphasic pattern of an early spike and fall, followed by a sustained gradual increase at both ages. First-phase (0-10 min) insulin secretion in the old rats was significantly lower at 150 (184 vs. 524 microU/min, P less than 0.05) and 220 mg/dl (327 vs. 644 microU/min, P less than 0.05), while it was nearly identical at 360 mg/dl. Although lower in the old rats, second-phase (11-50 min) insulin secretion was not statistically significantly different for each glucose level. When first- and second-phase insulin secretion rates were combined, the old rats' insulin secretion was only lower at the 150 mg/dl level (248 vs. 426 microU/min, P less than 0.05). Thus, at the more physiological glucose level, old rats showed a significantly lower response, while at the higher levels insulin secretion was similar. This diminishing age effect with increasing glucose dose suggests a defect in islet sensitivity to glucose rather than a diminished capacity to secrete insulin.

Aging↗

PubMed1985

Impact of age on weight goals.

Although the health hazards due to excessive obesity and excessive leanness are multiple and diverse, weight recommendations for over 40 years have been based solely on the risk of dying. The weight recommendation tables in nearly universal usage have been derived from the experience of the life insurance industry. Those tables have not recommended any weight adjustments for age. An analysis of the actuarial data on which the most recent tables are based shows that minimal mortality occurs at progressively increasing body weight as age advances (20 to 29, through 60 to 69 years). There is, furthermore, no systematic sex difference in those weights. We have prepared height-weight tables that are age-specific and delete sex and body frame type as variables. These weight standards are lower for young adults and higher for older adults than those previously recommended. A review of 23 other reported populations confirms the need to adjust weight standards for age.

Actuarial Analysis↗

PubMed1984

Association between blood pressure and the rate of decline in renal function with age.

A significant negative correlation (P less than 0.0001) exists between the mean blood pressure (MBP) and the rate of decline in creatinine clearance with time in years (BCr) in 446 subjects in the Baltimore Longitudinal Study on Aging (BLSA) followed serially on five or more visits over a period of 8 or more years. Even when the 118 subjects with possible renal and/or urinary tract pathology (category 1) and 74 subjects treated with diuretic and/or antihypertensive agents (category 2) were not included, this relationship remained in the 254 "normal" (category 3) subjects. Since both MBP and negativity of the BCr tend to increase with age, multiple regression analyses using both MBP and age as independent variables were performed to determine their respective influences on BCr. Both MBP and age significantly influenced BCr. When those subjects with hypertension (mean MBP greater than 107 mm Hg) were not included, however, the inverse relationship between MBP and BCr is lost, suggesting that an accelerated loss of renal function is observed primarily because of the impact exerted by individuals with blood pressures in the hypertensive range.

Adult↗

PubMed1984

The enteric enhancement of glucose-stimulated insulin release. The role of GIP in aging, obesity, and non-insulin-dependent diabetes mellitus.

The effect of aging, obesity, and non-insulin-dependent diabetes mellitus on glucose-stimulated gastric inhibitory polypeptide (GIP) levels was studied in 55 male subjects, ranging in age from 19 to 84 yr, and in obesity, expressed as body mass index, from 21 to 34. Studies were performed using the hyperglycemic glucose clamp technique, in which the blood glucose was maintained at 125 mg/dl above basal for 2 h. Glucose (40 g/m2 body surface) was ingested at 60 min. Plasma immunoreactive GIP (IR-GIP) did not change during intravenous (i.v.) glucose alone, but began to rise within 10 min after glucose ingestion and reached a peak at 30-40 min. Basal and stimulated IR-GIP levels were markedly elevated in diabetic subjects and modestly elevated in obese subjects, compared with appropriately matched controls. In contrast, age had little effect on plasma IR-GIP levels either in the basal state or after glucose ingestion. When IR-GIP responses to oral glucose were expressed as a relative change from basal levels, IR-GIP rose 86% in diabetic subjects and 243% in obese subjects, compared with 185% and 165% in their respective controls. IR-GIP rose 179% in young subjects and 144% in middle-aged subjects, while, in old subjects, the increase was 265%. Plasma IRI levels were reduced in the diabetic subjects, slightly elevated in obese subjects, and were similar in older and younger subjects. Beta cell sensitivity to endogenous GIP decreases with age, and is unchanged in both obesity and nonmedicated diabetes.

Adult↗

PubMed1983

A longitudinal study of nutritional intake in men.

Seven-day dietary diaries were provided by 180 male participants in the Baltimore Longitudinal Study of Aging during each of three time periods (1961 to 1965, 1966 to 1970, and 1971 to 1975). These men are a highly educated, upper-middle class group. At the time of their first diary, they were aged 35 to 74 years. The data were analyzed for aging, cohort, and time effects on diet by utilizing three types of research designs concurrently: cross-sectional, longitudinal, and time series. The nutrients considered were calories, protein, carbohydrate, fat, saturated fatty acids, polyunsaturated fatty acids, and cholesterol. Aging had a negative effect on intake of calories, fat, saturated fatty acids, and cholesterol. Cohort effects were not observed for any of these nutrients. Over time, intake of carbohydrates and cholesterol declined, while intake of polyunsaturated fatty acids rose.

Adult↗

PubMed1983

Prevention of the glucose intolerance of thiazide diuretics by maintenance of body potassium.

The effect of thiazide diuretics on the glucose tolerance of seven normal men in whom potassium loss was prevented with supplementation was studied using the glucose clamp technique. An initial control 2-h hyperglycemic clamp was performed to create a square wave of hyperglycemia 125 mg/dl above basal. At 1 h, 40 g glucose/m2 body surface area was ingested. Serial insulin (IRI) and gastric inhibitory polypeptide (GIP) levels were measured as well as the level of glucose infusion necessary to maintain the stable hyperglycemic level. After the initial study, subjects were placed on a 10-day course of 100 mg hydrochlorothiazide and 80 meq potassium per day. Subjects were monitored for dietary potassium intake, urinary potassium, and sodium losses, and the replacement of potassium adjusted accordingly. A repeat glucose clamp was done on day 10. When potassium losses were prevented, thiazides induced no alterations in glucose tolerance, beta-cell sensitivity to glucose, GIP-cell sensitivity to glucose, beta-cell sensitivity to GIP, or tissue sensitivity to insulin. Two control studies in which hypokalemia was allowed to ensue after hydrochlorothiazide ingestion revealed a diminution in glucose tolerance, a consequence of diminished pancreatic beta-cell response to glucose. We conclude that the thiazide effect on glucose tolerance is a consequence of the resultant hypokalemia that the diuretic may create.

Adolescent↗