Gait Seed and Sagittal Abdominal Diameter: The Results from the Handan Eye Study

The sagittal abdominal diameter (SAD) is more precise than body mass index (BMI) for predicting adverse events in elderly. While physical function and BMI is related, the relationship is uncertain. BMI and gait speed (GS) is related and have a U-shaped distribution. The objective was to examine the relationship between GS and SAD in men and women aged 50 years and older. This was a cross-sectional analysis. Data from the Handan Eye Study (HES), a Chinese prospective longitudinal study with participants randomly selected from the Yongnian county. Usual GS was measured over a 4 meters-track. SAD was categorized by interquartile: <18.0cm; 18.0-19.79cm; 19.8-21.89cm; ≥ 21.9cm. Unadjusted and adjusted analyses of covariance were performed to estimate the gender-specic means (and 95% CI) of GS (in m/s) according to SAD categories.


Results
The current analyses were performed in 2852 participants. Mean age was 56.16 years for women and (95%CI 0.923-0.973)]. After adjustment for age, the reported trends between GS and SAD in categories were largely con rmed in women, but not in men.

Conclusions
Age and gender should be considered when we explore the relationship between GS and SAD in elderly.

Background
Ageing and its associated social problems have turned into a common concern in many countries.
Physical function decline is the main component of ageing and also is critical risk factor for adverse events of ageing such as mortality, fall, disability, hospitalization [1]. Gait speed (GS) is a generally utilized estimation to assess to evaluate the physical function. Besides, GS has been viewed as a good predictor for death, cognitive impairment, depression and Alzheimer's disease in elderly [2].
Obesity is a prevalent disease in industrialized countries and has shown to signi cantly predict negative outcome. Other than clinical comorbidity, it is associated with subclinical conditions such as in ammation and oxidative damage. Body mass index (BMI) is a typical index to explore and classify obesity and be perceived as a marker in a few conditions such as systemic diseases, well-being and frailty, etc. In recent years, lots of studies uncovered that sagittal abdominal diameter (SAD) was a better indicator of cardiovascular disease, hypertension and diabetes than BMI and waist circumference [3,4].
Previous studies have explored the relationship between BMI and GS, which demonstrated U-shaped relationship [5,6], but not all studies a rmed reliably. No study has yet explored this relationship between SAD and GS in 50 years and older in a Chinese rural area.
Since BMI and GS are related and have a U-shaped distribution, we hypothesize that SAD (a better predictor than BMI) may also be associated with GS. Therefore, the purpose of this study is to explore whether SAD and GS are associated or not and to indicate their correlation types among village-dwelling older adults aged 50 years and older.

Data source and study population
The Handan Eye Study (HES) is a population-based longitudinal study in Handan, Hebei Province, China. In 2006-2007 subjects of 7557 individuals (response rate:90.4%) participated in the baseline study.
In 2012-2013, 5394 subjects (85.3 %) of the survivors took part in the follow up study. GS test was performed in subjects aged 50 years or above. A detailed description of the methodology used for the HES can be found in previous publications [7,8]. Beijing Tongren Hospital Ethics Committee (TREC2006-22) approved the HES according to the principles embodied in the Declaration of Helsinki and all participants provided written informed consent.
The data used in this study were collected from the HES follow-up study because SAD measurement was conducted only in the follow-up study. A comprehensive questionnaire, laboratory tests, an extensive eye examination procedure and an anthropomorphic procedure which included standing height, weight, SAD, waist circumference, hip circumference and blood pressure were undergone by trained nurses and examiners.
Sagittal Abdominal Diameter SAD was measured using a portable sliding-beam caliper (Holtain Ltd, Crymych, UK). Participants rested on a lightly padded bed in a exed position when the examiner marked the level of the iliac crests. The examiner lowered the caliper upper arm, lightly touching the abdomen. The SAD was recorded in duplicate to the nearest 0.1cm [9].

Gait Speed
Participants performed the 4-meter gait speed (GS) test according to standardized instructions [10].
Participants were asked to walk a distance of 4 meters at their usual pace, starting from a still position. Start the timer with the rst footfall after the 0-m line and stop the timer with the rst footfall after the 4m line.GS was operationalized as the ratio between distance and time, and expressed in meters by seconds (m/s).

Other Variables
A detailed interviewer-administered questionnaire which included socio-demographics, self-reported chronic diseases and living behaviors such as smoking, drinking was used. Diabetes and hypertension were de ned according to self-report from participants (previously diagnosed).

Statistical analysis
The data are presented as the means and standard deviations for continuous variables and as frequencies and percentages for categorical variables. All analyses were independently conducted for men and women to evaluate the gender differences for SAD. SAD was categorized by interquartile. Unadjusted and adjusted analyses of covariance were performed to assess the gender-speci c means (and 95% CI) of GS (in m/s) as indicated by SAD categories. After having provided results from the unadjusted analyses, age-adjusted models were performed. Spearman correlation coe cients were utilized to clarify the associations between SAD and GS. P-values<0.05 were considered statistically signi cant and 95% con dence intervals (95% CI) are provided. All analyses were performed using SPSS, version 24.0 (SPSS Inc., Chicago, IL, USA).

Results
Among the 5394 participants enrolled in the HES follow-up study, 3297 were aged 50 years or older. We choose the sample because SAD only performed in the HES follow-up study and GS test in elderly aged 50 years or above. The current analyses were performed in 2852 (86.5%) participants, after exclusion of 445 (13.5%) individuals with missing data for the main variables of interest (GS or/and SAD). There were no signi cant differences in BMI, waist circumference, systolic blood pressure, diastolic blood pressure, SAD and the status of diabetes, smoking, alcohol drinking between the two groups. GS and SAD were dramatically signi cantly correlated (r=-0.072, P = 0.00). Linear trends between SAD and GS were reported for women and men.

Discussion
In this cross-sectional analysis of persons aged 50 years and older, we found that GS follows a linear pattern across SAD categories. Compared to those in the lowest quartile of SAD (<18cm), participants in the highest quartile (>21.9cm) were more likely to have lower GS. These relationships are independent of age in women, but not in men.
BMI is utilized to con rm in case subjects are overweight or obese disregarding the distribution of body fat. High BMI is related with hypertension, diabetes mellitus and cardiovascular diseases. Abdominal adiposity is likewise a risk factor for the development of dyslipidemia, hypertension CVDs and glucose intolerance. Aggregating proof proposes that visceral adipose tissue is more emphatically identi ed with metabolic risk factors than subcutaneous adipose tissue. WC and SAD are utilized as abdominal obesity markers, yet WC doesn't recognize visceral from subcutaneous adipose tissue, and consequently can't precisely re ect levels of visceral adipose tissue. SAD gives a superior intra-abdominal or visceral obesity estimate than WC.
Our study revealed that the unadjusted means of GS decreased with increase of SAD. It presented a linear pattern both in men and in women and was con rmed by recent evidence. A few reports have shown that fatty in ltration of muscle is a signi cant part of low muscle strength and that abdominal obesity can lessen muscle strength through in ammatory and endocrine mechanisms [11][12][13]. Aging is associated with increased the in ammatory activity. Raised CRP levels have been related with incident mobility limitations in subjects with and without diabetes [14]. A new report found that WC was rmly associated with mobility disability and with activities of daily living disability and showed that obesity was associated with functional decline after some time [15].
We also found that the trend was largely con rmed in women, but not in men after adjustment for age. It is notable that ageing leads to reduction of functional ability and increase of visceral adipose tissue. Past studies have shown that body fat will redistribute and subcutaneous fat tissue will move to visceral adipose tissue with age [16]. The difference is partly explained by menopausal status. Several alterations in fat deposits occur with the advent of the menopause, leading to a change in the distribution of body fat. Postmenopausal women had a higher prevalence of central obesity [17].
The strengths of our study included that it provided the relationship between SAD and GS in a Chinese rural and village settings. However, there are some limitations in our study. First, the participants were recruited among persons aged 50 years and older living in rural areas. This may introduce a representativeness bias for external validation of our results. Second, non-participants were older and had more hypertension which could lead to selection biases. Third, no conclusion in regard to the cause or consequence can be drawn, due to the cross-sectional approach.

Conclusions
A linear relationship between gait speed and SAD is here demonstrated. After age adjustment, the relationship exists in women, not in men. It may provide complementary information in the comprehensive assessment of older persons. Age and gender should be considered when we explore the relationship between physical function and visceral adipose tissue in elderly.