Participants
A total of 1431 participants were recruited from the memory clinic of Shanghai Jiao Tong University Affiliated Sixth People’s Hospital and community in Shanghai. This study was approved by the Institutional Ethic Reviewing Board of Shanghai Jiao Tong University Affiliated Sixth People’s Hospital. Each subject had a uniform structured evaluation performed by a neurologist, which included a medical history inquiry and neurological examination. Inclusion criteria were: normal vision and hearing to complete cognitive tests; no history of alcoholism, drug abuse, and head trauma. The exclusion criteria of this cohort included aged ≤40 or above 90 years, low education level (≤5 years); presence of neurological or psychiatric antecedents; diseases involving the central nervous system; severe diseases such as cancer, kidney disease, chronic liver disease. Relevant laboratory tests were carried out to exclude metabolic disorders, nutritional deficiencies and infectious diseases which may be adversely affecting cognitive function, such as abnormalities in folic acid, vitamin B12, thyroid function, and rapid plasma regain or treponema pallidum particle agglutination. Cranial magnetic resonance imaging scanning was performed routinely to exclude any potential causes of cognitive decline, such as cerebral infarction, subdural hematomas, hydrocephalus, intracranial tumors and infections.
Neuropsychology
All participants received a comprehensive neuropsychological assessment, which were carried out by trained raters who were blind to diagnosis. Six neuropsychological tests in three cognitive domains were examined, AVLT 30-minute delayed free recall auditory verbal learning test (AVLT-N5) and AVLT recognition (AVLT-N7) for memory domain15; animal fluency test (AFT, total score) and 30-item Boston naming test (BNT, total score) for language domain16,17; shape trails test (STT), parts A and B (time to completion) for executive domain18. Mini-mental state examination (MMSE)19-21, Montreal cognitive assessment-basic (MoCA-BC) 22,23, and the third version of Addenbrooke’s Cognitive examination (Chinese version, ACE-III-CV)24 were also tested as global cognition. Activities of daily living (ADL) and functional activities questionnaire (FAQ) were used to assess functional capacity based on the reports of informants25,26. Each neuropsychological test has been standardized using published normative data, and widely used in China with good reliability and validity.
Measures
AD diagnosed based on the recommendations from the National Institute on Aging-Alzheimer’s Association (NIA-AA) workgroups27. MCI based on Bondi’s criteria as above5,6,28 , diagnosis of MCI was given if the participant met one of the following criteria: 1. impaired scores (defined as >1 standard deviation (SD) below the age-corrected normative mean) on two of the six neuropsychological indexes in the same cognitive domain (AVLT 30-minute delayed free recall and AVLT recognition for memory, AFT and BNT for language, STT-A and STT-B for executive function); 2. impaired scores (defined as >1 SD below the age-corrected normative mean) in each of the three cognitive domains. Individuals who did not meet all of these criteria and have no cognitive impairment were identified as normal individuals (NC).
Collection of clinical information
Height and body weight were measured, and body mass index (BMI) was calculated as weight/height2 (kg/m2). Handgrip strength (kg) was estimated through the dynamometer (WCS-100, Nantong, China). Participants were asked to squeeze the dynamometer for a practice trial using submaximal effort to determine their understandings on the procedure and the grip size adjustments. They were randomly assigned to start the test with their dominant or non-dominant hand. To complete the test, participants were asked to use one hand to squeeze the dynamometer as hard as possible, and repeat using the other hand for a total of three alternating hands. Similar to previous studies using this measure, we extracted the maximum value achieved using either hand as the summary measure29,30.
Statistical analysis
SPSS, version 19.0 (SPSS, Inc., Chicago, IL, USA) was used for statistical analysis. Based on a normality test, all variables for which the data were normally distributed are presented as mean ± standard deviation values, and skewed data are presented as median values with interquartile ranges, categorical variables are presented as percentages (%). Pair analyses were carried out using the paired Student’s t test and the Wilcoxon signed rank sum test. Intergroup comparisons of skewed data were conducted using the Kruskal-Wallis test. Spearman correlation analysis, logistic regression analysis, and multiple stepwise regression analysis were conducted to identify the associations between handgrip strength and cognitive function. A two-tailed P value of less than 0.05 was considered to be statistically significant. The receiver operating characteristic curve (ROC) was plotted to assess the power of the handgrip strength as a screening measure to discriminate AD and MCI.