Klotho, FGF21 and FGF23: Novel Pathways to Musculoskeletal Health?

Bone mineral density, muscle mass and physical function reach their peak between the second and fourth decade of life and then decline steadily with aging. The crucial question is: what factors contribute to or modulate this decline? The aim of this mini-review is to propose a theoretical framework for the potential role of emerging biomarkers such as klotho, fibroblast growth factors (FGF)21 and FGF23 on musculoskeletal health, with a particular focus on decline in muscle mass and function, and calls for future research to examine this proposed link. The identification of new physiological mechanisms underlying these declines may open a potentially important avenue for the development of novel intervention strategies aimed at preventing or reducing their potentially detrimental consequences.

Intake of antioxidants and subsequent decline in physical function in a racially/ethnically diverse population

OBJECTIVES

Oxidative stress is considered a risk factor for physical function (PF) decline with aging. The objective of this study was to examine the relationship between antioxidant intake and change in PF over a 5-year period.

DESIGN, SETTING, PARTICIPANTS

The Boston Area Community Health (BACH) Survey is a population-based longitudinal study including 5,502 racially/ethnically diverse and randomly selected participants aged 30-79 years.

MEASUREMENTS

In total, 2828 persons aged 30-79 years completed the validated Block Food Frequency Questionnaire (FFQ) and participated in the follow-up study. Change in PF from baseline (2002-2005) to follow-up (2006-2010) was assessed using the validated SF-12 questionnaire. Linear models were used to examine the association between energy-adjusted quartiles of vitamins C, E and carotenoids and change in PF.

RESULTS

A low intake (first quartile) of vitamin E was associated with a greater decline in PF compared with the highest quartile, with a mean difference in change in PF of -1.73 (95%CI:-3.31,-0.15). Notably, this mean difference was clinically meaningful as it was equivalent to the effect estimate we found for participants who were approximately 15 years apart in age in our cohort, as 1 year increase in age was associated with a mean difference in change in PF of -0.11 (95%CI:-0.16,-0.06). PF decline was not significantly different in the lowest compared with the highest quartile of vitamin C (mean difference=-1.29, 95%CI:-2.61, 0.03) or carotenoids (mean difference=-0.62, 95%CI:-2.22,0.99).

CONCLUSIONS

Low intake of vitamin E was significantly associated with decline in PF with aging. These results are clinically meaningful, extend previous findings that oxidative stress contributes to PF decline, and may inform the development of future prevention strategies aimed at reducing this clinical and public health problem.

Hip bone geometry in HIV/HCV-co-infected men and healthy controls

People with both HIV and hepatitis C are more likely than those with HIV alone to have wrist, hip, and spine fractures. We compared hip strength between HIV/HCV-co-infected men and healthy men and found that HIV/HCV-co-infected men had decreased hip strength due to lower lean body mass.

INTRODUCTION

Hepatitis C co-infection is a risk factor for fragility fracture among HIV-infected populations. Whether bone strength is compromised in HIV/HCV-co-infected patients is unknown.

METHODS

We compared dual-energy x-ray absorptiometry (DXA)-derived hip geometry, a measure of bone strength, in 88 HIV/HCV-co-infected men from the Johns Hopkins HIV Clinic to 289 men of similar age and race and without HIV or HCV from the Boston Area Community Health Survey/Bone Survey. Hip geometry was assessed at the narrow neck, intertrochanter, and shaft using hip structural analysis. Lean body mass (LBM), total fat mass (FM), and fat mass ratio (FMR) were measured by whole-body DXA. Linear regression was used to identify body composition parameters that accounted for differences in bone strength between cohorts.

RESULTS

HIV/HCV-co-infected men had lower BMI, LBM, and FM and higher FMR compared to controls (all p < 0.05). At the narrow neck, significant differences were observed between HIV/HCV-co-infected men and controls in bone mineral density, cross-sectional area, section modulus, buckling ratio, and centroid position. After adjustment for race, age, smoking status, height, and weight, only buckling ratio and centroid position remained significantly different between cohorts (all p < 0.05). Substituting LBM, FM, and FMR for weight in the multivariate model revealed that differences in LBM, but not FM or FMR, accounted for differences in all narrow neck parameters between cohorts, except buckling ratio and centroid position.

CONCLUSION

HIV/HCV-co-infected men have compromised hip strength at the narrow neck compared to uninfected controls, which is attributable in large part to lower lean body mass.

Relative contributions of multiple determinants to bone mineral density in men

SUMMARY

Focus on individual risk factors for osteoporosis could allocate disproportionate attention to trivial relationships. We tested many recognized risk factors of osteoporosis for their association with bone mineral density (BMD) in multivariate models among men. Lean mass accounted for the most variance, with substantially less accounted for by demographic, strength, and health factors.

INTRODUCTION

Osteoporosis in men has gained recognition as a public health problem, generating an interest in the search for risk factors. Isolation of individual risk factors could allocate disproportionate attention to relationships that may be of limited consequence.

METHODS

The Boston Area Community Health/Bone (BACH/Bone) Survey is a population-based study of randomly selected community-dwelling men (age, 30-79 years). BMD and lean mass were measured by dual X-ray absorptiometry. Socioeconomic status, health history, and lifestyle factors were obtained via interview. Hormone levels and markers of bone turnover were obtained from non-fasting blood samples. Multivariate analyses measured relative contributions of covariates to femoral neck (hip), one-third distal radius (wrist), and lumbar spine BMD.

RESULTS

Factors positively associated with BMD in multivariate models at the three sites were black race and appendicular lean mass. Asthma was consistently negatively associated. Various other risk factors also contributed significantly to each of the individual sites. R (2) values for the hip, wrist, and spine were 41%, 30%, and 24%, respectively. Lean mass accounted for the most explained variance at all three sites.

CONCLUSIONS

These data emphasize the limitation of focusing on individual risk factors and highlight the importance of potentially modifiable lean mass in predicting BMD.

Age trends in proximal femur geometry in men: variation by race and ethnicity

Data on bone architecture in diverse male populations are limited. We examined proximal femur geometry in 1,190 black, Hispanic, and white men. Cross-sectional analyses indicate greatest bone strength among black men, and greater age-related differences in bone strength among Hispanic men than other subjects at the narrow neck and intertrochanter regions of the proximal femur.

INTRODUCTION

Although race/ethnic differences in bone mass are well-documented, less is known about differences in bone architecture. We examined proximal femur geometry in a diverse, randomly-sampled population of 1,190 community-dwelling men (age 30-79 y).

METHODS

Dual X-ray absorptiometry scans were obtained for 355 black, 394 Hispanic, and 441 white subjects. Measures were obtained for the narrow neck (NN), intertrochanter (IT) and shaft regions of the proximal femur via hip structural analysis. Analyses considered bone mineral density (BMD, g/cm2), outer diameter (cm), cross-sectional area (CSA, cm2), section modulus (Z, cm3), and buckling ratio (BR). Results were adjusted for height, weight and physical activity level.

RESULTS

Black subjects exhibited greater age-specific BMD, CSA and Z, than their white counterparts. For instance, at age 50 y, NN BMD was approximately 11% higher among black men (p < 0.001). Hispanic men exhibited sharper age-related differences in NN and IT BMD than did others. IT BMD, for instance, decreased by 2.4% with 10 y age among Hispanic subjects, but had virtually no age trend in others (p < 0.001).

CONCLUSIONS

These results imply greater bone strength among black American men than among their white counterparts, and may indicate elevated fracture risk among older Hispanic American subpopulations.

The relationship between body composition and bone mineral content: threshold effects in a racially and ethnically diverse group of men

We examined BMC and body composition in 1,209 black, Hispanic, and white men. Weight, BMI, waist circumference, and fat mass were associated with BMC only up to certain thresholds, whereas lean mass exhibited more consistent associations. The protective influence of increased weight appears to be driven by lean mass.

INTRODUCTION

Reduced body size is associated with decreased bone mass and increased fracture risk, but associations in men and racially/ethnically diverse populations remain understudied. We examined bone mineral content (BMC) at the hip, spine, and forearm as a function of body weight, body mass index (BMI), waist circumference, fat mass (FM), and nonbone lean mass (LM).

METHODS

The design was cross-sectional; 363 non-Hispanic black, 397 Hispanic, and 449 non-Hispanic white residents of greater Boston participated (N = 1,209, ages 30-79 y). BMC, LM, and FM were measured by DXA. Multiple linear regression was used to describe associations.

RESULTS

Weight, BMI, waist circumference, and FM were associated with BMC only up to certain thresholds. LM, by contrast, displayed strong and consistent associations; in multivariate models, femoral neck BMC exhibited a 13% increase per 10 kg cross-sectional increase in LM. In models controlling for LM, positive associations between BMC and other body composition measures were eliminated. Results did not vary by race/ethnicity.

CONCLUSIONS

The protective effect of increased body size in maintaining bone mass is likely due to the influence of lean tissue. These results suggest that maintenance of lean mass is the most promising strategy in maintaining bone health with advancing age.

Race/ethnic differences in bone mineral density in men

The epidemiology of osteoporosis in male and minority populations is understudied. We compared BMD in 1,209 Black, Hispanic, and White men. Black men exhibited higher BMD than Hispanic or White men. Age-related BMD decreases were greatest among Hispanic men. Results may help explain variation in hip fracture rates by race/ethnicity.

INTRODUCTION

The epidemiology of osteoporosis in male and minority populations is understudied. To address this concern, we conducted a study of skeletal health in a diverse population of adult males.

METHODS

A total of 367 Black, 401 Hispanic, and 451 White men aged 30-79 years were randomly sampled from Boston, MA. Bone densitometry (bone area (BA), bone mineral content (BMC), and bone mineral density (BMD)) at the whole body, hip, lumbar spine, and forearm was performed. Multiple regression analyses on 1,209 men with available data were used to describe race/ethnic group-specific means (height- and age-adjusted) and age trends (height-adjusted) in BMC, BA, and BMD. Results were weighted to represent the Boston male population aged 30-79 years.

RESULTS

Black men had greater BMC and BMD than Hispanic or White men. Femoral neck BMD was 5.6% and 13.3% higher in Black men than in Hispanic and White men, respectively. Differences between Hispanic and White subjects were restricted to the hip. Age-related declines in BMC and BMD were significantly steeper among Hispanic than Black or White men.

CONCLUSIONS

Differences in BMC and BMD could explain variation in fracture rates among Black, Hispanic, and White men. The steeper age-related BMD decline in Hispanic men is of particular concern.

Testosterone level, androgen receptor polymorphism, and depressive symptoms in middle-aged men

BACKGROUND

Testosterone (T) level declines progressively with age. Psychiatric symptoms of T deficiency (e.g., dysphoria, fatigue, irritability, low libido) are also symptoms of depression, and appear to be variably expressed.

METHODS

We assessed independent measures of hypothalamic-pituitary-gonadal axis functioning, i.e., total T level and androgen receptor (AR) CAG repeat length (CAG RL), a genetic trait marker associated with AR function; and depression (diagnosed by above-threshold score on the Center for Epidemiologic Studies-Depression Scale [CES-D]) in 1000 men (mean age = 62.6 years; SD = 8.3) who participated in the Massachusetts Male Aging Study.

RESULTS

There were 110 (11%) men with "depression" (CES-D score > or = 16) in the analysis sample. Neither total T level nor CAG RL was associated with depression in bivariate analyses. Among men with shorter CAG RLs, the percentage of men with depression was 21.6% in the lowest subgroup of total T (defined by quintiles) and 4.2% in the highest subgroup of total T. This was confirmed in simple logistic regression models with depression as the dependent variable and continuous total T as the predictor, run separately within the three CAG RL subgroups: depression was significantly and inversely associated with total T in men with shorter CAG RLs but not in men with moderate and longer CAG RLs.

CONCLUSIONS

CAG isotype, a genetic trait marker of androgen receptor function, may mediate the expression of the central nervous system effects of T deficiency in men.

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

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

Relation between psychosocial risk factors and incident erectile dysfunction: prospective results from the Massachusetts Male Aging Study

Erectile dysfunction (ED) is recognized as a major public health problem. ED may be due to a wide range of factors, but recent work has focused on the medical and physical etiology of ED. The importance of psychosocial risk factors should not be dismissed, however, and several cross-sectional studies have reported associations between ED and depression, anger, and dominance. Whether these factors are prospectively associated with the risk of ED has yet to be established. Longitudinal data obtained from 776 respondents in the Massachusetts Male Aging Study (1987-1997) were used to examine whether the presence of depressive symptoms, the way in which anger was expressed, or the trait of dominance independently contributed to the risk of ED 8.8 years later. The results suggest that new cases of ED are much more likely to occur among men who exhibit a submissive personality. The implications of these findings are discussed.

Socioeconomic factors and incidence of erectile dysfunction: findings of the longitudinal Massachussetts Male Aging Study

Despite the well-documented relationship of socioeconomic factors (SEF) to various health problems, the relationship of SEF to erectile dysfunction (ED) is not well understood. As such, the goals of this paper are: (1) to determine whether incident ED is more likely to occur among men with low SEF; and (2) to determine whether incident ED varies by SEF after taking into consideration other well-established ED risk factors that are also associated with SEF such as smoking, diabetes, and high blood pressure. We used data from 797 participants in the longitudinal population-based Massachusetts Male Aging Study (baseline 1987-1989, follow-up 1995-1997) who were free of ED at baseline and had complete data on ED and all risk factors. ED was determined by a self-administered questionnaire and its relationship to SEF was assessed using logistic regression. We first analyzed the age-adjusted relationship of education, income, and occupation to incidence of ED. The results show that men with low education (O.R. = 1.46, 95% C.I. = 1.02-2.08) or men in blue-collar occupations (O.R. = 1.68, 95% C.I. = 1.16-2.43) are significantly more likely to develop ED. For the multivariate model, due to multicollinearity among education, income, and occupation, we ran three separate models. After taking into consideration all the other risk factors--age, lifestyle and medical conditions--the effect of occupation remained significant. Men who worked in blue-collar occupations were one and a half times more likely to develop ED compared to men in white-collar occupations (O.R. = 1.55, 95% C.I. = 1.06-2.28).

Measurement of erectile dysfunction in population-based studies: the use of a single question self-assessment in the Massachusetts Male Aging Study

A concise, reliable means of assessing erectile dysfunction (ED) in large, multidisciplinary population-based studies is needed. A single, direct question for self-assessed ED was assessed in the population-based sample of the Massachusetts Male Aging Study (MMAS). Of the 1156 respondents to the 1995-97 MMAS follow-up evaluation, 505 were randomly selected to complete either the International Index of Erectile Function (IIEF) (n = 254), or the Brief Male Sexual Function Inventory (BMSFI) (n = 251), in addition to the single question self-assessment. The proportion not classified due to missing data was MMAS-9%, BMSFI-8%, and IIEF-18%. The single question correlated well with these other measures (r = 0.71-0.78, P < 0.001). Prevalence was similar to that based on the IIEF, agreement was moderate (kappa = 0.56-0.58), and associations with previously identified risk factors were similar for each classification. Thus, the MMAS single question may be a practical tool for population-based studies where detailed clinical measures of ED are impractical.

Erectile dysfunction and coronary risk factors: prospective results from the Massachusetts male aging study

BACKGROUND

Erectile dysfunction (ED), a wide spread and troublesome condition among middle-aged men, is partly vascular in origin. In the Massachusetts Male Aging Study, a random-sample cohort study, we investigated the relationship between baseline risk factors for coronary heart disease and subsequent ED, on the premise that subclinical arterial insufficiency might be manifested as ED.

METHODS

Men ages 40-70, selected from state census lists, were interviewed in 1987-1989 and reinterviewed in 1995-1997. Data were collected and blood was drawn in participants' homes. ED was assessed from responses to a privately self-administered questionnaire. Analysis was restricted to 513 men with no ED at baseline and no diabetes, heart disease, or related medications at either time.

RESULTS

Cigarette smoking at baseline almost doubled the likelihood of moderate or complete ED at followup (24% vs. 14%, adjusted for age and covariates, P = 0.01). Cigar smoking and passive exposure to cigarette smoke also significantly predicted incident ED, as did overweight (body-mass index > or =28 kg/m(2)) and a composite coronary risk score. Weaker prospective associations were seen for hypertension and dietary intake of cholesterol and unsaturated fat.

CONCLUSIONS

Erectile dysfunction and coronary heart disease share some behaviorally modifiable determinants in men who, like our sample, are free of manifest ED or predisposing illness. Open questions include whether modification of coronary risk factors can prevent ED and whether ED may serve as a sentinel event for coronary disease.

Incidence of erectile dysfunction in men 40 to 69 years old: longitudinal results from the Massachusetts male aging study

PURPOSE

We estimated the incidence of erectile dysfunction in men 40 to 69 years old at study entry during an average 8.8-year followup, and determined how risk varied with age, socioeconomic status and medical conditions.

MATERIALS AND METHODS

Data from a randomly sampled population based longitudinal study of Massachusetts men were analyzed. A total of 1,709 men completed the baseline interview during 1987 to 1989 and 1,156 survivors completed followup from 1995 to 1997. The analysis sample consisted of 847 men without erectile dysfunction at baseline and with complete followup information. Erectile dysfunction was assessed by discriminant analysis of 13 questions from a self-administered sexual function questionnaire and a single global self-rating question.

RESULTS

The crude incidence rate for erectile dysfunction was 25.9 cases per 1,000 man-years (95% confidence interval [CI] 22.5 to 29.9). The annual incidence rate increased with each decade of age and was 12.4 cases per 1,000 man-years (95% CI 9.0 to 16.9), 29.8 (24.0 to 37.0) and 46.4 (36.9 to 58.4) for men 40 to 49, 50 to 59 and 60 to 69 years old, respectively. The age adjusted risk of erectile dysfunction was higher for men with lower education, diabetes, heart disease and hypertension. Population projections for men 40 to 69 years old suggest that 17,781 new cases of erectile dysfunction in Massachusetts and 617,715 in the United States (white males only) are expected annually.

CONCLUSIONS

Although prevalence estimates and cross-sectional correlates of erectile dysfunction have recently been established, incidence estimates were lacking. Incidence is necessary to assess risk, and plan treatment and prevention strategies. The risk of erectile dysfunction was about 26 cases per 1,000 men annually, and increased with age, lower education, diabetes, heart disease and hypertension.

Incidence of erectile dysfunction in men 40 to 69 years old: longitudinal results from the Massachusetts male aging study

PURPOSE

We estimated the incidence of erectile dysfunction in men 40 to 69 years old at study entry during an average 8.8-year followup, and determined how risk varied with age, socioeconomic status and medical conditions.

MATERIALS AND METHODS

Data from a randomly sampled population based longitudinal study of Massachusetts men were analyzed. A total of 1,709 men completed the baseline interview during 1987 to 1989 and 1,156 survivors completed followup from 1995 to 1997. The analysis sample consisted of 847 men without erectile dysfunction at baseline and with complete followup information. Erectile dysfunction was assessed by discriminant analysis of 13 questions from a self-administered sexual function questionnaire and a single global self-rating question.

RESULTS

The crude incidence rate for erectile dysfunction was 25.9 cases per 1,000 man-years (95% confidence interval [CI] 22.5 to 29.9). The annual incidence rate increased with each decade of age and was 12.4 cases per 1,000 man-years (95% CI 9.0 to 16.9), 29.8 (24.0 to 37.0) and 46.4 (36.9 to 58.4) for men 40 to 49, 50 to 59 and 60 to 69 years old, respectively. The age adjusted risk of erectile dysfunction was higher for men with lower education, diabetes, heart disease and hypertension. Population projections for men 40 to 69 years old suggest that 17,781 new cases of erectile dysfunction in Massachusetts and 617,715 in the United States (white males only) are expected annually.

CONCLUSIONS

Although prevalence estimates and cross-sectional correlates of erectile dysfunction have recently been established, incidence estimates were lacking. Incidence is necessary to assess risk, and plan treatment and prevention strategies. The risk of erectile dysfunction was about 26 cases per 1,000 men annually, and increased with age, lower education, diabetes, heart disease and hypertension.

Diet and sex hormone-binding globulin

The serum concentration of sex hormone-binding globulin (SHBG) is inversely related to weight and in animal studies is inversely related to protein intake. As SHBG can affect the biological activity of testosterone and estradiol, we wished to determine the role of protein intake on SHBG levels in men. Using data from the Massachusetts Male Aging Study we examined cross-sectional relationships between dietary components and SHBG levels in 1552 men (aged 40-70 yr) for whom these factors were known. Analyzed by multiple regression, controlling for testosterone and estradiol levels, age (P<0.001) and fiber intake (P = 0.02) were positively correlated to SHBG concentration, whereas body mass index (P<0.001) and protein intake (P<0.03) were negatively correlated to SHBG concentration. The intakes of calories, fat (animal or vegetable), and carbohydrate were not related to SHBG concentration. We conclude that age and body mass index are major determinants of SHBG concentrations in older men, and fiber and protein intake are also significant contributors to SHBG levels, but total caloric intake and the intake of carbohydrate or fat are not significant. Thus, diets low in protein in elderly men may lead to elevated SHBG levels and decreased testosterone bioactivity. The decrease in bioavailable testosterone can then result in declines in sexual function and muscle and red cell mass, and contribute to the loss of bone density.

The relationship between depressive symptoms and male erectile dysfunction: cross-sectional results from the Massachusetts Male Aging Study

OBJECTIVE

Studies have shown that there is an association between depression and male erectile dysfunction (MED). However. these earlier studies suffer considerable methodological flaws including: a) lack of a multidisciplinary approach; b) poor sampling techniques; and finally, c) poor and variable measures of MED and depression. Our objectives are: a) to determine whether MED is associated with depressive symptoms and b) to determine whether this association is independent of aging and para-aging factors.

METHOD

Data were obtained from the Massachusetts Male Aging Study (MMAS). The MMAS was a cross-sectional, population-based multidisciplinary survey of health in normally aging men (aged 40-70 years) conducted from 1986 to 1989. In the analytic model, depressive symptoms, as measured by a score of 16 or greater on the Center for Epidemiological Studies-Depression (CES-D) scale, was used as a predictor of MED, which was assessed with a self-administered questionnaire.

RESULTS

MED was associated with depressive symptoms after controlling for potential confounders (odds ratio (OR) 1.82, 95% confidence interval (Ct) 1.21-2.73).

CONCLUSIONS

We conclude that the relationship between depressive symptoms and MED in middle-aged men is robust and independent of important aging and para-aging confounders, such as demographic, anthropometric and lifestyle factors, health status, medication use, and hormones.