Season of birth and dementia: Findings from Chinese elderly based on a nationwide data

Abstract

Objectives Previous studies showed inconsistent results regarding the association between season of birth and dementia later in life. Evidence has mainly come from developed countries with relatively homogeneous geographical features. In this study, we examined the association between season of birth and dementia among Chinese elderly as well as geographical region‐specific and urban/rural‐specific patterns. Methods We utilized data from the Second China National Sample Survey on Disability in 2006, and employed multivariate logistic regression to estimate the association between dementia and birth seasonality. We conducted subsample analyses by urbanity and geographical region. Results This study included 354 859 Chinese elderly aged 60 and above. Compared with the summer‐born, the odds of dementia were significantly lower among those born in winter (OR: 0.82, 95% CI: 0.70, 0.96). Similar associations were also found in urban and northern subsamples. Conclusion Winter birth was associated with a lower prevalence of dementia in old age, especially among those living in urban and northern areas of China. This association further suggests the critical role of early life period and environment on health in later life.

Season-of-birth phenomenon in health and longevity: epidemiologic evidence and mechanistic considerations

“…39 In Chinese elderly aged 60 and above, the risk for dementia was shown to be substantially lower among those born in winter than that for the summer-born. 40 These findings, however, have not been confirmed in studies conducted in other Northern Hemisphere countries, where no evidence for seasonality of birth in AD patients was found. [41][42][43][44] No seasonal pattern was also observed in the Southern Hemisphere (Australia) (Henderson et al, 1991).…”

Season of birth and the risk of dementia in the population‐based Rotterdam Study

“…So far, studies that assessed the relationship between environmental exposures early in life and dementia or AD, using season of birth as a proxy, showed inconsistent results [ 13 – 19 , 4 , 20 , 21 ]. Small sample size and a discrepancy between the population from which the cases were selected and the reference population, may have led to these varying results.…”

“…This difference was statistically significant when adjusting for age, sex and major vascular risk factors of dementia Tolppanen et al [ 20 ] Finland 70,719 AD cases 282,862 age, sex and region-of-residence matched controls Summer: OR = 1.03 (95% CI 1.00–1.05) e No strong evidence that month or season of birth is related to risk of AD, although summer births (June–August) were associated with higher odds of AD compared to winter births. However, the absolute difference was only 0.5% (31.7% vs. 32.2%) Ding et al [ 21 ] China 1326 354,859 respondents of the Second China National Sample Survey on Disability, aged 60 years and older OR = 0.76 (95% CI 0.65–0.90) f Winter birth was associated with a lower prevalence of dementia, especially among those living in urban and northern areas of China AD Alzheimer’s disease, CI confidence interval, OR odds ratio, RR relative risk a Results are shown for observed dementia births (cases with and without family history combined) versus expected dementia births (based on reference population) during the first quarter of the year, unless specified differently b Risk ratio for AD comparing 1st quarter birth to birth during rest of the year, adjusted for age, sex and education c Adjusted expected birth frequency based on population currently living in the area d Odds ratio for dementia among winter born (Dec.–Feb.) compared to summer born (Jun.–Aug.…”

“…Season of birth has repeatedly been used as a proxy for the effect of several environmental exposures early in life on the risk of brain diseases later in life, including Parkinson’s disease, multiple sclerosis and schizophrenia [ 7 – 12 ]. Previous studies on season of birth and dementia generally show ambiguous results and are described in Table 1 [ 13 – 19 , 4 , 20 , 21 ].…”

Season of birth and biomarkers of early‐life environment

“…Children born in winter were more likely to be preterm compared with those born in spring (Lee, Steer, & Filippi, 2006), and also had the lowest birth weights (Lawlor, Leon, & Smith, 2005), the highest levels of innate immune cells, (Thysen et al, 2016), and the greatest odds of high IgE when compared to summer births (Susanto et al, 2017). People born in autumn had a higher risk of asthma (Knudsen et al, 2007), allergy (Lockett et al, 2016), cardiovascular diseases (Tornhammar et al, 2014), and those born in winter had a lower risk of dementia (Ding, He, Song, & Zheng, 2019). However, individuals born in autumn lived longer than those born in spring (Doblhammer & Vaupel, 2001;Ueda, Bonamy, Granath, & Cnattingius, 2013;Vaiserman, Collinson, Koshel, Belaja, & Voitenko, 2002).…”