Difficulty of falling asleep and non-high-density lipoprotein cholesterol level among Canadian older adults: a cross-sectional analysis of the Canadian Longitudinal Study for Aging baseline data

OBJECTIVETo examine whether difficulty of falling asleep (DoFA) is associated with non-high-density lipoprotein cholesterol (non-HDL-C) level among Canadian older adults.METHODS26,954 individuals aged 45–85 years from the baseline data of the Canadian Longitudinal Study for Aging were included in this study. DoFA was categorized into five groups by answer to the question “Over the last month, how often did it take you more than 30 min to fall asleep?” Response options are “Never, < 1 time/week, 1−2 times/week, 3−5 times/week, or 6−7 times/week”. Non-HDL-C, the difference of total cholesterol and HDL-C, were categorized into five categories based on these cut-offs (< 2.6 mmol/L, 2.6−3.7 mmol/L, 3.7−4.8 mmol/L, 4.8−5.7 mmol/L, and ≥ 5.7 mmol/L). Ordinal logistic regression (logit link) continuation ratio models were used to estimate the odds of higher non-HDL-C levels for DoFA status. Adjusted means of non-HDL-C by DoFA status were estimated by general linear models. All analyses were sex separately using analytic weights to ensure generalizability.RESULTSThe proportions of DoFA in five categories were 41.6%, 25.7%, 13.6%, 9.4%, 9.7% for females and 52.9%, 24.9%, 10.5%, 6.1%, 5.6% for males, respectively. After adjustment of demographical and other covariates (such as depression, comorbidity, sleeping hour, etc.) compared to those who reported never having DoFA, the ORs (95% CIs) of higher levels of non-HDL-C for those whose DoFA status in < 1 time/week, 1−2 times/week, 3−5 times/week, and 6−7 times/week were 1.12 (1.05−1.21), 1.09 (0.99−1.18), 1.20 (1.09−1.33), 1.29 (1.17−1.43) in females and 1.05 (0.98−1.13), 0.95 (0.87−1.05), 1.21 (1.08−1.37), 0.97 (0.85−1.09) in males, respectively. The adjusted means of non-HDL-C among the five DoFA status were 3.68 mmol/L, 3.73 mmol/L, 3.74 mmol/L, 3.82 mmol/L, 3.84 mmol/L for females and 3.54 mmol/L, 3.58 mmol/L, 3.51 mmol/L, 3.69 mmol/L, 3.54 mmol/L for males, respectively.CONCLUSIONSThe results of this study have identified a risk association pattern between DoFA status and non-HDL-C levels in females but not in males. Further research is needed to confirm these findings.

The increased level of non-high-density lipoprotein cholesterol (non-HDL-C) is a reliable risk predictor for future coronary heart disease (CHD).^[1–3] Evidence from studies of the relationship between non-HDL-C reduction and CHD risk has suggested that non-HDL-C is an important target of therapy for CHD prevention.^[4] Non-HDL-C, the difference between total cholesterol (TC) and HDL-C, includes low-density lipoprotein cholesterol (LDL-C), intermediate-density lipoprotein cholesterol, and very-low-density lipoprotein cholesterol; they are all proatherogenic lipoproteins containing apolipoproteins B (Apo B).^[5] Currently, LDL-C is the primary target of treatment of CHD since it contains the majority of Apo B and lowering its level reduces CHD risk.^[6] However, LDL-C level in clinic is most likely estimated indirectly and its levels depend on fasting status and the levels of triglycerides.^[7] The level of non-HDL-C is not related to triglycerides measurement and not affected by fasting status, thus, it is considered superior to LDL-C as a treatment target for CHD risk management. Sleep disorders are conditions that changes the way people sleep and affects the overall health and quality of life. In a study conducted among 2,000 Canadians aged 18 years or older, 40.2% of individuals reported having either trouble falling or staying asleep, or early morning awakening for at least three nights per week in a previous month.^[8] Serious sleep disorders not only affects persons’ life quality,^[9,10] and increases risk for motor vehicle accidents,^[11] but also found to be associated with an increased risk for cardiovascular diseases (CVD).^[12–14] Sleep disturbance was observed to be highly associated with the increased risk of CVD, it was considered as a potential risk predictor of CVD.^[13] However, whether sleep disorders are associated with dyslipidemia is uncertain since studies showed contradictory results.^[15] Short sleep duration was found to be associated with an increased risk of CVD,^[16,17] but there is no conclusion whether sleep duration is linked to dyslipidemia.^[18] Furthermore, there is no study examined the relationship between sleep disorders and non-HDL-C levels. Therefore, the aim of this study is to examine how sleep disturbance is associated with lipid profile, particularly the levels of non-HDL-C among older adults. To explore this association, we used the baseline data collected by the Canadian Longitudinal Study on Aging (CLSA), a large population-based cohort study.