年龄和受教育年限与简易精神状态量表评分的非线性相关关系:一项以西安市鄠邑区40岁及以上农村人群为基础的横断面调查

Objective: To investigate the relationship of age and years of schooling with the Mini-mental State Examination (MMSE) scores among the aged 40 years or above in rural areas of Xi'an, China. Methods: From October 2014 to March 2015, subjects who lived in a village in the suburbs of Xi'an, China, were selected as the research samples. MMSE was performed to assess their global cognitive function. At the same time, we collected the data about demographic information, living habits, medical history, family history, physical examination, and biochemical examination. The relationship of age and years of schooling with MMSE scores was analyzed by simple median regression analysis, multivariate median regression analysis, and stratified analysis. Results: We enrolled for the study a total of 1 799 subjects, including 726 (40.35%) males, 1 613 (89.66%) subjects aged 40-69 years, and 186 (10.34%) subjects aged ≥70 years. The average age was 55.52±9.93 years. Of them, 222 (12.34%) subjects were illiterate, 568 (31.57%) subjects received 1-6 years of schooling, and 1 009 (56.09%) subjects received ≥ 7 years of schooling. The median MMSE score (25% quantile, 75% quantile) was 27 (24, 29). Regarding the relationship between MMSE score and age, multivariate median regression analysis was performed to correct the confounding factors, which showed that in the subjects aged 40-69 years old, the median MMSE score decreased by 0.06 points (β=-0.06, P<0.001) for every 1 year of age increase, while that was 0.34 points decrease (β=-0.34, P=0.001) in the subjects aged ≥70 years old. That is, with the increase of age, the decline rate of MMSE score was higher in people aged ≥70 years old than that in the subjects aged 40-69 years old. The similar non-linear correlation was found in subgroups such as male, female, illiterate, 1-6 years of schooling; while in the subjects with ≥7 years of schooling, such relationship was not certain, due to the small sample size of 30 subjects in the group with both aged ≥ 70 years and ≥ 7 years of schooling. As for the relationship between MMSE score and years of schooling, the multivariate median regression analysis showed that in the subjects with 0-6 years of schooling, the median MMSE score increased by 0.86 points (β=0.863, P<0.001) for each additional year of schooling, while that was 0.16 points of increase (β=0.16, P<0.001) in the subjects with ≥7 years of schooling. That is, with the increase of years of schooling, the growth rate of MMSE scores was higher in people with 0-6 years of schooling than in people with ≥ 7 years of schooling. The similar relationship existed in the subgroups such as male, female, aged 40-69 years old; while in the subjects aged ≥ 70 years old, such relationship was not certain, due to the small sample size in the group with both aged ≥ 70 years and ≥ 7 years of schooting. Based on the analyses above, the median MMSE score expectation equation was established in four subgroups according to age and years of schooling: (1) aged 40-69 years old and 0-6 years of schooling: MMSE = 22.00 + 0.20 × gender (female: 0; male: 1) + 0.00 × age (value 40-69 years old) + 0.80× years of schooling (value 0-6 years); (2) aged 40-69 years old and ≥ 7 years of schooling: MMSE=30.18 + 0.08 × gender (female: 0; male: 1) - 0.08 × age (value 40-69 years old) + 0.17× years of schooling (value 7-15 years); (3) aged ≥ 70 years old and 0-6 years of schooling: MMSE=43.67+1.33 × gender (female: 0; male: 1) - 0.33× age (value 70-85 years old) + 0.78 × years of schooling (value 0-6 years); (4) aged ≥ 70 years old and ≥ 7 years of schooling: MMSE = 52.43 + 3.34 × gender (female: 0; male: 1) - 0.41× age (value 70-85 years old) ) -0.16 × years of schooling (values 7-15 years). The reliability of the prediction equation for the subjects with both aged ≥ 70 years old and ≥ 7 years of schooling needs to be verified due to the small sample size. Results: In the population aged 40 or above in rural areas of Xi'an, China, with the increase of age, the rate of decline of MMSE score was higher in people aged ≥ 7weo0 years old than that in those aged 40-69 years old. As the years of schooling increase, the growth rate of MMSE scores is higher in people with 0-6 years of schooling than in people with ≥7 years of schooling.