Timing of peak bone mass in Caucasian females and its implication for the prevention of osteoporosis. Inference from a cross-sectional model.

To determine the timing of peak bone mass and density, we conducted a cross-sectional study of bone mass measurements in 265 premenopausal Caucasian females, aged 8-50 yr. Bone mass and bone mineral density were measured using dual X-ray absorptiometry and single-photon absorptiometry at the spine (anteroposterior, lateral), proximal femur, radius shaft, distal forearm, and the whole body. Bone mass parameters were analyzed using a quadratic regression model and segmented regression models with quadratic-quadratic or quadratic-linear form. The results show that most of the bone mass at multiple skeletal locations will be accumulated by late adolescence. This is particularly notable for bone mineral density of the proximal femur and the vertebral body. Bone mass of the other regions of interest is either no different in women between the age of 18 yr and the menopause or it is maximal in 50-yr-old women, indicating slow but permanent bone accumulation continuing at some sites up to the time of menopause. This gain in bone mass in premenopausal adult women is probably the result of continuous periosteal expansion with age. Since rapid skeletal mineral acquisition at all sites occurs relatively early in life, the exogenous factors which might optimize peak bone mass need to be more precisely identified and characterized.

Putting body weight and osteoporosis into perspective.

Osteoporosis is characterized by a reduction in bone mineral density (BMD). Women more than men are at risk for osteoporosis-related fractures, especially in the wrists, lumbar spine, and hips. Numerous diet and lifestyle factors, including body weight, influence BMD, and in turn, fracture risk. BMD in the total body, hip, lumbar spine, and radius is weakly to moderately correlated to body weight, fat mass, and lean body mass in adolescent, perimenopausal, and elderly women, possibly as the result of stress on the skeleton from the mechanical loading of body weight alone. In addition, greater lean body mass may be a cause. Other explanations include increased hormonal circulation in obese women and greater conversion of adrenal androgens to estrogens linked to greater mass of adipose tissue. Currently no value is agreed on for weight-to-height versus osteoporosis and related fracture risk, but some extra fat mass yielding a body mass index > 26-28 does confer limited protection, whereas a slender figure yielding a body mass index < 22-24 increases risk.

Wrist, spine, and hip bone density in women with variable histories of lactation.

This study investigated the relationship between long-term lactation (greater than or equal to 10 m/child) and bone density in women aged 26-37. The subjects either experienced long-term lactation for 1-2 children (n = 10), long-term lactation for 3-4 children (n = 8), or were nulliparous (n = 10). The three groups did not differ significantly in height, weight, percent of ideal weight, usual caffeine and calcium intake, or duration of oral contraceptive use. Bone-density measurements were obtained by single- or dual-photon absorptiometry from the ultradistal radius, lumbar spine (L2-L3), and three hip sites: femoral neck, Ward's triangle, and trochanteric. Lactation history was not associated with significant differences in bone density in any bone site. With respect to height, weight, Ca intake, and duration of lactation, only height was correlated to bone density and only for L2-L3 (r = 0.48, p less than 0.02). Thus, a history of long-term lactation may not be associated with low peak adult bone density.

Effect of diets high in butter, corn oil, or high-oleic acid sunflower oil on serum lipids and apolipoproteins in men.

This randomized blind crossover study compared serum lipid and apolipoprotein concentrations in 20 men consuming 37-43% of energy as fat from diets based on corn oil, high-oleic acid sunflower oil, and butter. Each phase of the crossover design included 2 wk of butter-based diet followed by 5 wk of designated vegetable-oil-based diet with a 7-wk washout period between phases. Compared with values for the butter-based diet, the vegetable-oil-based diets reduced serum total cholesterol by 16-21% (p less than 0.001), LDL cholesterol by 21-26% (p less than 0.001), triglycerides by 10-21% (p less than 0.01 for the higher figure), and apolipoprotein B-100 by 22-29% (p less than 0.001). When values fell, they fell further on the corn-oil-based diet. There were no significant changes in serum HDL cholesterol or apolipoprotein A-1. These data suggest that when men on diets high in saturated fatty acids reduce their saturated fatty acid intake but not their total fat intake, many can still experience a significant lowering in serum total cholesterol.

The effect of lactation on peak adult shaft and ultra-distal forearm bone mass in women.

The effect of long-term vs short-term lactation (three to four children with an average of 10.7 mo vs 2.8 mo duration for each child) on maternal forearm bone-mass sites that are either primarily trabecular or cortical in composition was determined. The habitual calcium intake of each subject exceeded 90% of her recommended dietary allowance (RDA) for nonpregnant, pregnant, and lactating states. Trabecular and cortical bone mass were estimated using single-photon densitometry at ultra-distal and midshift sites on the radius, respectively. Bone mass at both sites was lower in the long-term than in the short-term lactation group and, at the ultra-distal site (trabecular bone), the effect was statistically significant (p less than 0.05). These data indicate that even when women consume the RDA for calcium, long-term lactation can deplete ultra-distal bone mass in the forearm.

Influence of calcium intake and growth indexes on vertebral bone mineral density in young females.

This cross-sectional study examined the relationship between current calcium intake and vertebral bone mineral density (V-BMD) in 49 healthy Caucasian adolescent females aged 8-18 y. The ability of current calcium intake to account for the variance in V-BMD in this population was compared with that seen with weight, height, maturational age (determined by the Tanner Sexual Maturity Rating), chronological age, and total energy expenditure. Calcium intake was determined from the mean of 4-d, food-intake records. Average vertebral bone mineral density from L1-L4 was measured by dual x-ray absorptiometry. A multiple-regression model revealed that 81% of the variance in V-BMD was described by maturational age, chronological age, and calcium intake, with all representing significant predictors of bone mineral density (P less than 0.0001, 0.005, 0.04, respectively). This study supports the hypothesis that better calcium nutrition during adolescence may optimize, within genetic boundaries, peak bone mass.

Effects of diets high in saturated fatty acids, canola oil, or safflower oil on platelet function, thromboxane B2 formation, and fatty acid composition of platelet phospholipids.

Platelet function and fatty acid composition were investigated in 30 healthy male subjects who ate a controlled-saturated-fatty-acid (baseline) diet for 3 wk and then consumed either safflower oil or canola oil as a major fat source for 8 wk. Fatty acid composition of platelet phospholipids reflected changes in dietary fatty acid composition. Compared with baseline a 35% decrease (P less than 0.05) in arachidonic acid was observed in platelet phospholipids of the canola-oil diet group while long chain n-3 fatty acids rose 7-26% (P greater than 0.05). Compared with baseline both unsaturated-fatty-acid diets reduced platelet aggregation at 3 wk of oil-based diet feeding (P less than 0.01) whereas only canola oil influenced platelet function (lowered ATP secretion) at 8 wk (P less than 0.01). No significant difference was observed in thromboxane B2 concentrations between oil-treatment groups at 8 wk. Both oil-based diets had short-term beneficial effects on platelet function but the effect of canola oil persisted longer.

Serum lipid and apolipoprotein concentrations in healthy men on diets enriched in either canola oil or safflower oil.

This randomized, blind study measured changes in serum lipid and apolipoprotein concentrations in 16 men consuming 39 +/- 1% of energy (en%) as fat either from safflower- or canola-oil-based diets for 8 wk. Initially, the men were stabilized for 3 wk on a typical American (baseline) diet. Compared with baseline, the vegetable-oil-based diets reduced serum total cholesterol 9-15% (P less than 0.002), low-density-lipoprotein (LDL)-cholesterol 12-20% (P less than 0.002), and apolipoprotein B-100 21-24% (P less than 0.001). There were no significant changes from baseline to the end of the study in serum triglycerides, total high-density-lipoprotein (HDL) cholesterol, HDL3 cholesterol, HDL2 cholesterol, or apolipoprotein A-I. These data suggest that even if total fat intake remains at 39-40 en%, many men show lowered LDL cholesterol if saturated fatty acid intake is minimized and that diets high in polyunsaturated fatty acids do not necessarily lower HDL-cholesterol concentrations.

Relative effects on serum lipids and apolipoproteins of a caprenin-rich diet compared with diets rich in palm oil/palm-kernel oil or butter.

Two randomized, blind studies measured changes in serum cholesterol, other serum lipids, and apolipoprotein (apo) concentrations in hypercholesterolemic men consuming caprenin (Cap)-rich diets after either baseline diets enriched in palm oil/palm-kernel oil (PO/PKO) or butter. The triglyceride Cap contains 45% 22:0 and 50% 8:0-10:0. Compared with baseline values established at 3 wk on the PO/PKO diet, the 17 subjects on the Cap diet showed significant reductions after 6 wk in HDL cholesterol (HDL-C), HDL2-C, and HDL3-C and a significant increase in the ratio of total cholesterol, LDL-C, triglycerides, apo B-100, or apo A-I were seen. Compared with baseline values established at 3 wk on the butter diet, after 6 wk the seven subjects receiving the Cap diet showed no significant changes in the lipid and apolipoprotein indexes analyzed. These data show that one or more of 8:0, 10:0, and 22:0 fatty acids can contribute to hypercholesterolemia in men.

Assessing the cancer risk from foods.

Assessing the carcinogenicity of a compound and then determining what dosage is appropriate for human beings is a complex process. Carcinogens act either by altering deoxyribonucleic acid (DNA) or by promoting the growth of already altered cells. Carcinogenicity is evaluated with the use of structural analysis, in vitro mutagenesis assays, epidemiological findings, and dose-response studies in laboratory animals. In the animal studies, high doses are administered. Once a compound is found to be carcinogenic, the dose that will pose an acceptable cancer risk to human beings--one in a million--must be extrapolated from the high-dose data. This virtually safe dose (VSD) will be the allowable dosage for human contact. The extrapolation from high-dose animal studies to a VSD for human beings is based on the models for carcinogenic mechanisms. Debate exists as to how many interactions with DNA the carcinogen must have to initiate neoplastic growth and whether there exists a threshold for carcinogenic action below which there is no risk of cancer. The extrapolation model that is chosen greatly affects the VSD. Knowing how this extrapolation to a VSD is done will help dietitians better understand how allowable levels for carcinogens in foods are determined.

Putting osteoporosis in perspective.

Osteoporosis is characterized by a reduction in bone mineral density (BMD). Dietary patterns that encourage adequate calcium intake are essential to maximal development and later maintenance of bone mass. The majority of white women are at risk for osteoporosis-related fractures, especially in the wrist, spine, and hip. The degree of fracture risk at a specific bone site is best assessed by measuring BMD with single- or x-ray-photon absorptiometry. BMD in adults of any age is quite variable. Numerous diet and lifestyle factors influence BMD and, in turn, fracture risk. Sufficient evidence exists for a relationship between BMD and diet, particularly calcium and vitamin D; amenorrhea; body weight; alcoholism; smoking; and physical inactivity. Less convincing evidence exists for a relationship with dietary protein, dietary phosphorus, and caffeine intake. To minimize fracture risk, young women should have regular menses, consume a nutritionally adequate diet (according to the principles of the Food Guide Pyramid), perform regular physical activity, only consume a moderate intake of alcohol (if any), and not smoke. Postmenopausal women should follow those same guidelines and should seriously consider estrogen replacement therapy. Elderly persons especially should ensure adequate calcium and vitamin D nutriture. Currently, osteoporosis is the rule, rather than the exception, in old age for many white women. Dietitians can help reduce the prevalence of this disorder.

What characterizes elderly women who overuse vitamin and mineral supplements?

This study has identified some potentially important characteristics of elderly women who overuse vitamin and mineral supplements. These women tended to live alone and to have medical problems. The supplements were usually self-prescribed and purchased in a drugstore. The sources of information that supported supplement use were primarily the print media and family and friends rather than health professionals. Other studies have made similar findings. The degree of IHLC orientation failed to predict the amount of supplement use, although IHLC was shown to be useful in a recent study that included both young and elderly women. Thus, from our perspective, the identification of possible overusers of supplements should begin with elderly women who have health problems and live alone; point-of-purchase information should be targeted to drugstores. In this study and in other, either the actual reasons for supplement use were often inappropriate or the diets were adequate in many of the vitamins taken by supplements, such as vitamins A and C. Thus, education for elderly women that stresses the appropriate reasons for nutrient supplement use is clearly needed so that a correct link between nutrition need and use always is maintained. The high IHLC scores suggest that the majority of women in this study want to make their own decisions about their health. Given better information, overusers of supplements might instead choose a more reasonable approach for improving their diets. Dietitians/nutritionists were not usually used as a source of nutrition information by the elderly women in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between nutrient intake, body mass index, menstrual function, and ballet injury.

The effects of inadequate nutrition, menstrual dysfunction, and low body weight on the injury rate of ballerinas were studied. Forty-nine female ballet dancers, mean age 18.7 years, completed food frequency and injury questionnaires. Subjects were placed in one of two groups: those with an intake less than 70% of the Recommended Dietary Allowances (RDA) for key nutrients and those with an intake greater than 70% of the RDA for key nutrients. Sixty-nine percent of the dancers had intakes less than 70% of the RDA and were randomly assigned to either a vitamin/mineral supplement or to placebo for 6 months. The remaining dancers with diets adequate (greater than 70% RDA) in key nutrients received no treatment. All groups were questioned monthly about the incidence, severity, and nature of ballet injuries. Information regarding menses and height and weight was obtained. There were no significant differences in the severity or type of injuries among the dancers in the supplement, placebo, or no treatment groups. Dancers with abnormal menses had more bone injuries (mean = 15.00) than normally menstruating dancers (mean = 4.97) (p less than .05). Dancers with a Body Mass Index less than 19.0 spent more days with a low-grade injury (mean = 24.05) than dancers with a greater BMI (mean = 11.63) (p less than .05). There appears to be a relationship between dance injuries and both BMI and menstrual function.

Effect of aerobic training on diabetic nephropathy in a rat model of type 2 diabetes mellitus.

The effect of aerobic exercise intervention on the renal functional and ultrastructural changes associated with diabetes mellitus were studied in the obese Zucker rat, a rat model of type 2 diabetes. The obese Zucker rats began training at 18 wk of age (n=8) and were compared to obese sedentary controls (n=12) and lean sedentary nondiseased littermates (n=10). Body weight, kidney weight, serum creatinine, urine creatinine, creatinine clearance, urine IgG, urine IgG/creatinine ratio, urine total protein, urine albumin, urine albumin/creatinine ratio, glycated hemoglobin, serum fructosamine, fasting serum glucose, serum insulin, serum total cholesterol, serum triglycerides, blood pressure, and morphometric analyses of cortical glomeruli by light microscopy and electron microscopy were performed to evaluate renal function, structure, and metabolic control. The exercise training consisted of treadmill running, 5 da/wk for 1 hr/da. Exercise intervention lowered the body weight (p <0.05), reduced the percentage of glycated hemoglobin (p <0.05), and diminished the urine albumin concentration (p <0.05), compared to the obese sedentary controls. Exercise intervention did not significantly affect morphometric indices of renal ultrastructure. This study shows that aerobic exercise intervention significantly improved metabolic control and reduced albuminuria in a rat model of type 2 diabetes.

Hyperglycemia associated with high, continuous infusion rates of total parenteral nutrition dextrose.

A retrospective study was performed to determine whether there is an increased incidence of hyperglycemia in patients not predisposed to hyperglycemia (n = 102) who receive total parenteral nutrition (TPN) dextrose in excess of 4 to 5 mg/kg/min. Of the 37 subjects administered dextrose at > 5 mg/kg/min, 18 exhibited hyperglycemia. None did so who received dextrose at < or = 4 mg/kg/min (n = 19). TPN dextrose infusion rate was positively correlated with blood glucose concentration, over and above other variables considered in a multiple regression, including kcal/kg administered, furosemide or dopamine use, gender, age, or diagnosis. Thus, TPN dextrose infusion rates > 4 to 5 mg/kg/min increase risk of hyperglycemia.

The effect of ouabain on basal and thyroid hormone-stimulated muscle oxygen consumption.

In vivo triiodothyronine treatment (T3) increased soleus muscle oxygen consumption (QO2) when measured in vitro. Ouabain significantly decreased T3-induced muscle QO2, but not basal muscle QO2. Ouabain-sensitive metabolic processes in muscle, which essentially represents Na-K-ATPase activity, accounted for approximately 85% of the increased energy utilization by muscles that was caused by T3 treatment.

Oxygen consumption and oxidative capacity of hepatocytes from young male obese and nonobese Zucker rats.

The contribution of the liver to the increased metabolic efficiency of the obese rat (fa/fa) was examined. Oxygen consumption of isolated hepatocytes and isolated mitochondria, and hepatic activities of mitochondrial enzymes were measured. Hepatocyte oxygen consumption was similar in the obese and nonobese rats for all substrates tested. Mitochondrial respiration also was similar in both phenotypes for all substrates tested. Activities of citrate synthase, succinate dehydrogenase, and cytochrome oxidase were similar for obese and nonobese rats. Taken together, these data show that in vitro hepatic oxygen consumption and oxidative capacity are similar in obese and nonobese rats. Rates of mitochondrial respiration with palmitoylcarnitine further show that the capacity for hepatic lipid oxidation is similar in obese and nonobese rats. Therefore, the increased metabolic efficiency of the obese rat probably cannot be attributed to an intrinsic decreased hepatic oxidative capacity. Further, there is no defect in hepatic lipid oxidative capacity in the young obese rat.

Oxygen consumption and oxidative capacity of muscles from young obese and nonobese Zucker rats.

The contribution of muscle tissue to the increased metabolic efficiency of the obese (fa/fa) Zucker rat at 6 wk of age was examined. In vitro O2 consumption was similar in obese and nonobese soleus and extensor digitorum longus (EDL) muscles, whether the animals were fed ad libitum, fasted, or treated with triiodothyronine. No phenotypic difference in the in vitro O2 consumption was seen when the muscles were preincubated with or without exogenous insulin. Pyruvate kinase, citrate synthase, succinate dehydrogenase, and cytochrome oxidase activities were similar in the soleus and the EDL muscles of both phenotypes. Phosphofructokinase and lactate dehydrogenase activities were higher in the soleus muscles from the obese rats, whereas hexokinase activities were higher in the EDL muscles from the nonobese rats. Mitochondrial and whole muscle homogenate respiration rates were similar in both phenotypes. The soleus and EDL muscles from the obese animals weighed less than those from the nonobese, but empty carcass weights were similar. Taken together these data suggest that muscle mass, muscle O2 consumption, and muscle oxidative capacity are similar in 6-wk-old obese and nonobese rats. Therefore other tissues are probably responsible for the increased metabolic efficiency of the young obese rat.

Effect of treadmill training on muscle oxidative capacity and accretion in young male obese and nonobese Zucker rats.

This study was designed to determine if treadmill training of the male obese Zucker rat could reverse its deficit in muscle accretion, expose a possible latent defect in its muscle oxidative capacity or significantly alter its food intake and lipid deposition. At 12 wk of age muscle mass and myofibrillar protein concentration were significantly lower and body lipid and food intake were significantly higher in the sedentary obese than in the nonobese rat. Exercise, by both inducing hypophagia and increasing energy output, led to a lower body weight, body lipid, and muscle mass in the exercised than in the nonexercised rats. This response to exercise did not differ between both phenotypes, except for body lipid. In that case the reduction of body lipid was greater for the obese rats. Muscle mitochondrial enzyme activities and rates of mitochondrial respiration in the obese rats were not different or greater than those of their sedentary or pair-exercised nonobese counterparts. Taken together these data indicate that oxidative capacity per unit of muscle is not significantly lower in the obese rats than in nonobese rats in both sedentary and exercised states, but that total muscle oxidative capacity is lower on a whole-animal basis since total muscle mass is lower. Further, exercise reduces, but does not prevent the enhanced weight gain and lipid accretion that characterizes the obese rat.

Emergence of coherent transport in UBe13: an optical investigation in both the normal and superconducting states.

The far-infrared reflectance of heavy-fermion superconductor UBe13 has been measured from 0.5 K in the superconducting state, to 300 K. Coherent transport, characterized by an optical conductivity that exhibits a renormalized Drude peak at low frequencies, emerges between 45 and 85 K although the dc resistivity of UBe13 continues to increase with decreasing temperature down to approximately 2.5 K. In the superconducting state, the low frequency scattering rate falls abruptly, implying that the formation of the condensate alters dramatically the interaction between the heavy electrons.