Sex differences in the association of thigh fat and metabolic risk in older adults

A greater ratio of thigh subcutaneous fat to abdominal fat is associated with protection against non-alcoholic fatty liver disease

Background & Aims

No prospective studies have examined the association between thigh subcutaneous fat distribution and non-alcoholic fatty liver disease (NAFLD). We investigated the associations of thigh subcutaneous fat distribution with incidence and remission of NAFLD in a community-based prospective cohort.

Methods

We followed 1,787 subjects, who underwent abdominal ultrasonography, abdominal and femoral magnetic resonance imaging scans, and anthropometric assessments. Associations of thigh subcutaneous fat area/abdominal fat area ratio and thigh circumference/waist circumference ratio with incidence and remission of NAFLD were estimated using the modified Poisson regression model.

Results

Over a mean 3.6-year follow-up, 239 incident cases of NAFLD and 207 regressed cases of NAFLD were identified. Increasing thigh subcutaneous fat area/abdominal fat area ratio was associated with a lower risk of incident NAFLD and a higher likelihood of remission of NAFLD [risk ratio (RR) per SD: 0.69, 95% CI 0.59-0.81; 1.20, 95% CI 1.07-1.34, respectively). Each one SD increase in thigh circumference/waist circumference ratio was associated with a 16% lower risk of incident NAFLD (RR 0.84, 95% CI 0.76-0.94) and a 22% higher likelihood of remission of NAFLD (RR 1.22, 95% CI 1.11-1.34). Additionally, the effects of thigh subcutaneous fat area/abdominal fat area ratio on the incidence and remission of NAFLD were mediated through adiponectin (14.9% and 26.6%), homeostasis model assessment of insulin resistance (9.5% and 23.9%), and triglyceride (7.5% and 19.1%).

Conclusions

These results demonstrated that a favourable fat distribution, characterised by a greater ratio of thigh subcutaneous fat to abdominal fat, had a protective role against NAFLD.

Impact and implications

The associations of thigh subcutaneous fat distribution with NAFLD incidence and remission have not been prospectively examined in a community-based cohort. Our findings suggest that greater thigh subcutaneous fat relative to a given amount of abdominal fat has a protective effect against NAFLD among the middle-aged and older Chinese populations.

Multisystem physiological perspective of human frailty and its modulation by physical activity

"Frailty" is a term used to refer to a state characterized by enhanced vulnerability to, and impaired recovery from, stressors compared with a nonfrail state, which is increasingly viewed as a loss of resilience. With increasing life expectancy and the associated rise in years spent with physical frailty, there is a need to understand the clinical and physiological features of frailty and the factors driving it. We describe the clinical definitions of age-related frailty and their limitations in allowing us to understand the pathogenesis of this prevalent condition. Given that age-related frailty manifests in the form of functional declines such as poor balance, falls, and immobility, as an alternative we view frailty from a physiological viewpoint and describe what is known of the organ-based components of frailty, including adiposity, the brain, and neuromuscular, skeletal muscle, immune, and cardiovascular systems, as individual systems and as components in multisystem dysregulation. By doing so we aim to highlight current understanding of the physiological phenotype of frailty and reveal key knowledge gaps and potential mechanistic drivers of the trajectory to frailty. We also review the studies in humans that have intervened with exercise to reduce frailty. We conclude that more longitudinal and interventional clinical studies are required in older adults. Such observational studies should interrogate the progression from a nonfrail to a frail state, assessing individual elements of frailty to produce a deep physiological phenotype of the syndrome. The findings will identify mechanistic drivers of frailty and allow targeted interventions to diminish frailty progression.

Four pleiotropic loci associated with fat mass and lean mass

BACKGROUND

Fat mass and lean mass are two biggest components of body mass. Both fat mass and lean mass are under strong genetic determinants and are correlated.

METHODS

We performed a bivariate genome-wide association meta-analysis of (lean adjusted) leg fat mass and (fat adjusted) leg lean mass in 12,517 subjects from 6 samples, and followed by in silico replication in large-scale UK biobank cohort sample (N = 370 097).

RESULTS

We identified four loci that were significant at the genome-wide significance (GWS, α = 5.0 × 10-8) level at the discovery meta-analysis, and successfully replicated in the replication sample: 2q36.3 (rs1024137, pdiscovery = 3.32 × 10-8, preplication = 4.07 × 10-13), 5q13.1 (rs4976033, pdiscovery = 1.93 × 10-9, preplication = 6.35 × 10-7), 12q24.31 (rs4765528, pdiscovery = 7.19 × 10-12, preplication = 1.88 × 10-11) and 18q21.32 (rs371326986, pdiscovery = 9.04 × 10-9, preplication = 2.35 × 10-95). The above four pleiotropic loci may play a pleiotropic role for fat mass and lean mass development.

CONCLUSIONS

Our findings further enhance the understanding of the genetic association between fat mass and lean mass and provide a new theoretical basis for their understanding.

Android fat as a determinant of metabolic syndrome: Sex differences

OBJECTIVES

Regional fat accumulation may play an important role in the pathogenesis of metabolic syndrome (MetS) and cardiovascular diseases, yet the results are controversial. The aim of this study was to determine the relationship between regional fat accumulation and MetS as well as the underlying mechanism in Chinese adults.

METHODS

We conducted a cross-sectional study of 428 Chinese adults (166 men and 262 women). Android and gynoid fat percentage (AFP and GFP) were measured by dual energy x-ray absorptiometry. Fasting lipid parameters were analyzed by chemistry analyzer COBAS.

RESULTS

Forty-six (28%) men and 34 (13%) women had MetS according to the modified National Cholesterol Education Panel Adult Treatment Panel III definition for South Asia. AFP was strongly correlated with more metabolic risk factors than GFP in men. In women, AFP and GFP showed significant opposite effects on triacylglycerol, high-density lipoprotein cholesterol, and waist circumference. On multivariate regression, AFP was an independent determinant of MetS in men after adjustment for confounding factors. For women, both AFP and the homeostatic model assessment for insulin resistance were predictors for MetS.

CONCLUSIONS

Increased android fat may play a direct role in the development of MetS in Chinese adults. However, the associations between android fat, insulin resistance, and MetS are sex-dependent. This is probably due to different effects of sex hormones on adipose tissue or by genetic factors between sexes. Knowing the sex differences in developing MetS may help design sex-specific preventive strategies that will benefit the overall population health.

Echocardiographic evaluation of left ventricular diastolic dysfunction in subclinical hypothyroidism: A case-control study

PURPOSE

To study the prevalence of left ventricular diastolic dysfunction (LVDD) in patients with subclinical hypothyroidism (SCH) and the response of LVDD to L-thyroxine therapy.

MATERIALS AND METHODS

This cross-sectional case-control study with one longitudinal arm included 67 patients with SCH attending a tertiary care hospital in Uttarakhand, India, and 67 age- and sex-matched healthy controls. LVDD was assessed by 2D, pulsed-wave Doppler (PWD), continuous wave Doppler (CWD), and tissue Doppler echocardiography (TDE). Patients with LVDD received L-thyroxine therapy with reassessment for LVDD 6 months later.

RESULTS

SCH patients had a higher prevalence of LVDD than controls (13.43% versus 1.49%; p = 0.017). LVDD showed a significant association with gender (p = 0.004) and serum FT4 (p = 0.001). E velocity, E' velocity, A' velocity, iso-volumetric relaxation time (IVRT), E/A, and E'/A' ratios were significantly lower, while A velocity, deceleration time (DT), E/E' ratio, left atrial (LA) volume index, and peak tricuspid regurgitation (TR) velocity were significantly higher in cases than controls (p < 0.05 each). The E/A ratio correlated significantly with age, serum very low-density lipoprotein (VLDL), triglycerides (TG), thyroid stimulating hormone (TSH), free triiodothyronine (FT3), and high-density lipoprotein (HDL) (p < 0.05 each). E' velocity correlated significantly with age, serum total cholesterol, VLDL, and TG (p < 0.05 each), DT with serum total cholesterol (p = 0.047), and LA volume index with age (p = 0.021). Age (p = 0.016) and serum HDL (p = 0.029) were independent predictors of E/A ratio. Gender was an independent predictor for LVDD (p = 0.003). Echocardiographic indices for LVDD showed significant improvement after 6 months of L-thyroxine therapy (p < 0.05 each).

CONCLUSIONS

LVDD occurs commonly in SCH patients. It can be detected timely using echocardiography and may be reversed by L-thyroxine therapy.

Gender and Age Impacts on the Association Between Thyroid Function and Metabolic Syndrome in Chinese

The relationship between thyroid dysfunction and metabolic syndrome (MS) is complex. We aimed to explore the impact of gender and age on their association in a large Chinese cohort. This cross-sectional study enrolled 13,855 participants (8532 male, 5323 female), who self-reported as healthy without any known previous diseases. Clinical data including anthropometric measurements, thyroid function, and serum metabolic parameters were collected. The associations between thyroid function and MS of both genders were analyzed separately after dividing thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and age into subgroups. MS risks were calculated by binary logistic regression models. Young males had significantly higher MS prevalence than females, yet after menopause, females had higher prevalence than males. Females had higher incidence of thyroid dysfunction than males. By using TSH quartiles as the categorical variables and the lowest quartile as reference, significantly increased MS risk was demonstrated in quartile 4 for males, yet quartiles 3 and 4 for females. By using FT3 quartiles as the categorical variables, significantly increased MS risk was demonstrated in quartile 2 to 4 for females only. By using age subgroups as the categorical variables, significantly increased MS risk was shown in both genders, with females (4.408-58.455) higher than males (2.588-4.943). Gender and age had substantial influence on thyroid function and MS. Females with high TSH and high FT3 had higher MS risks than males. Aging was a risk for MS, especially for females. Urgent need is necessary to initiate interventional programs.

Sex-differences of the healthy infra-patellar (Hoffa) fat pad in relation to intermuscular and subcutaneous fat content--data from the Osteoarthritis Initiative

The infra-patellar fat pad (IPFP) is composed of intra-articular adipose tissue; it represents a potential source of pro-inflammatory cytokines and has been associated with osteoarthritis of the knee. Yet, to what extent the size of the IPFP differs between healthy men and women, and how sex differences compare to those in inter-muscular and subcutaneous fat tissue content is unknown. We studied healthy reference subjects from the Osteoarthritis Initiative, without knee pain, without radiographic signs or without risk factors of femorotibial osteoarthritis. Sagittal magnetic resonance images (MRIs) of 99 right knees were used to segment the IPFP; in a subset, axial images of the thigh were available to segment inter-muscular and subcutaneous fat. Healthy men (n=40) displayed a 41% greater (p<0.001) IPFP volume and a 9% greater (p<0.01) ratio of IPFP volume/body weight than women (n=59). Men (n=13) displayed 15% greater intermuscular fat content (not significant), and a 50% lesser (p<0.01) subcutaneous fat content than women (n=12); when related to total thigh cross-sectional areas, these sex differences were +2% (not significant) and -53% (p<0.001). This is the first study to explore quantitative measures of the IPFP in healthy men and women, and to relate these to sex differences of inter-muscular and subcutaneous fat tissue content. Men displayed a significantly greater ratio of IPFP volume/body weight than women, similar amounts of inter-muscular fat, and strikingly less subcutaneous fat. These data provide a basis for further systematic studies of the variability of the IPFP with the body mass index and its role in knee osteoarthritis.

Ageing, adipose tissue, fatty acids and inflammation

A common feature of ageing is the alteration in tissue distribution and composition, with a shift in fat away from lower body and subcutaneous depots to visceral and ectopic sites. Redistribution of adipose tissue towards an ectopic site can have dramatic effects on metabolic function. In skeletal muscle, increased ectopic adiposity is linked to insulin resistance through lipid mediators such as ceramide or DAG, inhibiting the insulin receptor signalling pathway. Additionally, the risk of developing cardiovascular disease is increased with elevated visceral adipose distribution. In ageing, adipose tissue becomes dysfunctional, with the pathway of differentiation of preadipocytes to mature adipocytes becoming impaired; this results in dysfunctional adipocytes less able to store fat and subsequent fat redistribution to ectopic sites. Low grade systemic inflammation is commonly observed in ageing, and may drive the adipose tissue dysfunction, as proinflammatory cytokines are capable of inhibiting adipocyte differentiation. Beyond increased ectopic adiposity, the effect of impaired adipose tissue function is an elevation in systemic free fatty acids (FFA), a common feature of many metabolic disorders. Saturated fatty acids can be regarded as the most detrimental of FFA, being capable of inducing insulin resistance and inflammation through lipid mediators such as ceramide, which can increase risk of developing atherosclerosis. Elevated FFA, in particular saturated fatty acids, maybe a driving factor for both the increased insulin resistance, cardiovascular disease risk and inflammation in older adults.

Association of regional body fat with metabolic risks in Chinese women

OBJECTIVE

To investigate the association of regional fat depots with metabolic risk factors in Chinese women.

DESIGN

Total and regional fat depots including android fat and gynoid fat were measured by dual-energy X-ray absorptiometry. Central fat distribution was defined as android:gynoid fat ratio. Metabolic risk factors were defined as elevated TAG, reduced HDL-cholesterol, elevated blood pressure and elevated fasting plasma glucose. Logistic regression analyses were performed to examine the associations of regional fat depots with metabolic risk factors. The odds ratios of metabolic risks were further calculated according to tertiles of android fat and gynoid fat.

SETTING

Participants were recruited from a community-based cross-sectional study. Face-to-face questionnaires, anthropometric and dual-energy X-ray absorptiometry measures were conducted.

SUBJECTS

Chinese women (n 609) aged 18-79 years.

RESULTS

Android fat and android:gynoid fat ratio were associated with significantly increased odds (OR = 1·4-3·7; P < 0·01) for almost all risk factors, whereas gynoid fat was independently associated with significantly decreased odds (OR = 0·3-0·6; P < 0·01). The inverse associations of gynoid fat with metabolic risk factors remained after adjusting for android fat. Even if their android fat level was in high, women in the highest tertile of gynoid fat had lower odds of having at least two metabolic risk factors compared with women in the lowest gynoid fat tertile (P for trend < 0·01).

CONCLUSIONS

There were opposite associations of android and gynoid fat with metabolic risks in Chinese women. Gynoid fat rather than android fat might be a more important inclusion in metabolic disease risk evaluation in female Asians.

Central fat accumulation associated with metabolic risks beyond total fat in normal BMI Chinese adults

OBJECTIVE

To investigate the association of central fat with metabolic risks in normal BMI Chinese people.

METHODS

Normal BMI subjects (18.5 ≤ BMI < 24, n = 520) aged 18-82 years were included. Blood pressure, triglycerides, high-density lipoprotein cholesterol and fasting plasma glucose were collected as metabolic risk factors. Dual-energy X-ray absorptiometry was used to measure total and central fat. Central fat was indicated as percent trunk fat (%TF) and android/gynoid fat ratio. Multiple adjusted regression models were applied to investigate the association of total and central fat with metabolic risk factors. The assessment values of these fat measures were further compared by receiver-operating characteristic (ROC) curves.

RESULTS

Both total and central fat were correlated with metabolic risk factors. After adjusting for BMI, the significant association of percent body fat (%BF) with metabolic risks diminished, whereas %TF and android/gynoid fat ratio were still correlated. When BMI was replaced with %BF in the models, the results remained unchanged. ROC analysis showed the areas under the curve (AUCs) of total and central fat for at least two metabolic risk factors were comparable in men. However, in women, the AUCs of %TF and android/gynoid fat ratio were significantly greater than those of BMI, %BF and waist circumference.

CONCLUSIONS

Central fat accumulation had a stronger association with metabolic risks than total fat in normal BMI Chinese adults, particularly in women. Central fat had more important implications in assessing 'metabolically obese' individuals among normal BMI subjects.

The Official Positions of the International Society for Clinical Densitometry: Indications of Use and Reporting of DXA for Body Composition

The technique of body composition by dual-energy X-ray absorptiometry (DXA) has been used for several years in the research environment. Its ability to accurately and precisely measure lean, fat, and mineral composition in various body compartments has been well validated. Furthermore, the technique is widely available to clinical patients on existing DXA instruments throughout the world through the use of specific software packages and scanning algorithms. There have been few clear statements regarding the clinical indications for body composition measurement in patients outside the research setting. This is in part because of the lack of specific documented interventions that would be affected by body composition test results, beyond usual clinical advice. We have examined a few of the most common, specific scenarios (HIV therapy, sarcopenia, bariatric surgery, obesity) and proposed indications for body composition assessment. We have also discussed contraindications to body composition testing.

Lower thigh subcutaneous and higher visceral abdominal adipose tissue content both contribute to insulin resistance

It is well known that visceral adipose tissue (VAT) is associated with insulin resistance (IR). Considerable debate remains concerning the potential positive effect of thigh subcutaneous adipose tissue (TSAT). Our objective was to observe whether VAT and TSAT are opposite, synergistic or additive for both peripheral and hepatic IR. Fifty-two volunteers (21 male/31 female) between 30 and 75 years old were recruited from the general population. All subjects were sedentary overweight or obese (mean BMI 33.0 ± 3.4 kg/m(2)). Insulin sensitivity was determined by a 4-h hyperinsulinemic-euglycemic clamp with stable isotope tracer dilution. Total body fat and lean body mass were determined by dual X-ray absorptiometry. Abdominal and mid-thigh adiposity was determined by computed tomography. VAT was negatively associated with peripheral insulin sensitivity, while TSAT, in contrast, was positively associated with peripheral insulin sensitivity. Subjects with a combination of low VAT and high TSAT had the highest insulin sensitivity, subjects with a combination of high VAT and low TSAT were the most insulin resistant. These associations remained significant after adjusting for age and gender. These data confirm that visceral excess abdominal adiposity is associated with IR across a range of middle-age to older men and women, and further suggest that higher thigh subcutaneous fat is favorably associated with better insulin sensitivity. This strongly suggests that these two distinct fat distribution phenotypes should both be considered in IR as important determinants of cardiometabolic risk.

Mindfulness Intervention for Stress Eating to Reduce Cortisol and Abdominal Fat among Overweight and Obese Women: An Exploratory Randomized Controlled Study

Psychological distress and elevated cortisol secretion promote abdominal fat, a feature of the Metabolic Syndrome. Effects of stress reduction interventions on abdominal fat are unknown. Forty-seven overweight/obese women (mean BMI = 31.2) were randomly assigned to a 4-month intervention or waitlist group to explore effects of a mindfulness program for stress eating. We assessed mindfulness, psychological distress, eating behavior, weight, cortisol awakening response (CAR), and abdominal fat (by dual-energy X-ray absorptiometry) pre- and posttreatment. Treatment participants improved in mindfulness, anxiety, and external-based eating compared to control participants. Groups did not differ on average CAR, weight, or abdominal fat over time. However, obese treatment participants showed significant reductions in CAR and maintained body weight, while obese control participants had stable CAR and gained weight. Improvements in mindfulness, chronic stress, and CAR were associated with reductions in abdominal fat. This proof of concept study suggests that mindfulness training shows promise for improving eating patterns and the CAR, which may reduce abdominal fat over time.