Our important finding was not only the confirmation of APOs as a risk factor for EVA in young women, but also the finding that this risk is age-dependent, that is, the risk decreased with increasing age. More importantly, healthy behaviors can reduce the risk of APO-induced EVA.
Our study confirmed that APOs are risk factors for the development of EVA in women aged < 50 years with a low absolute risk of ASCVD. Compared with that in the non-APO group, the OR value (95% CI) for the occurrence of EVA in the APOs group was 1.67 (1.29–2.16). In addition, among different APOs, HDP and GD had the strongest role in increasing the risk of EVA, with OR values of 1.76 and 2.07, respectively. Although we did not find similar results, previous studies have reported that APOs are risk factors for the development of hypertension in women, with an OR (95% CI) of 2.4 (1.8–3.1) [31]. Because the degree of arterial stiffness is highly correlated with SBP, the increased risk of hypertension caused by APOs indirectly supports APOs as potential risk factors for arterial stiffness. In addition, Kaess et al. [32] and our previous study [33] found that the increase in arterial stiffness precede the increase in blood pressure and that arterial stiffness was the cause of hypertension. Therefore, APOs may induce hypertension by causing arterial stiffness.
We not only confirmed that APOs are a risk factor for EVA but also found that the increased risk of APO-induced EVA is age dependent. With increasing age, the risk of APO-induced EVA decreased from 2.51 in the 20- to 29-year age group to 1.35 in the 40- to 49-year age group. Our finding is similar to the observation that the risk of hypertension caused by APOs decreases with increasing age. Behrens et al. [34] found that the risk of hypertension caused by APOs decreased from 5.78 in the < 30-year age group to 2.26 in the ≥ 50-year age group. The increased risk of EVA and hypertension due to non-APOs with increasing age may be responsible for these findings.
Except for HDP and GD, we did not find that preterm birth or low birth weight alone was a risk factor for EVA. However, the risk of APO-induced EVA increases when the above 3 adverse outcomes are present concurrently (Table S5), which also suggests that the risk of APO-induced EVA may be dose-dependent. This finding is also similar to the increased risk of hypertension caused by APOs [31].
A healthy lifestyle is the cornerstone of the prevention of and improvements in chronic noncommunicable diseases. Our study verified the importance of a healthy lifestyle. Although the 4 health factors all reduced the risk of APO-induced EVA, the effect of low salt was more pronounced, which is consistent with the strong association between salt and arterial stiffness. A meta-analysis confirmed that restricting salt intake can reduce arterial stiffness [35]. Previous studies showed that a high-salt diet reduced the expression of endothelial nitric oxide synthase [36] and damages the glycocalyx sodium barrier of vascular endothelium [37], which in turn increases vascular stiffening.
Because MAP and the use of antihypertensive drugs are closely associated with arterial stiffness, in addition to adjusting for traditional confounding factors, we also further adjusted for the above factors to increase the reliability of the study results. Since no uniform standard for the definition of EVA has been established, we redefined EVA using different percentiles and found that APOs remained a risk factor for EVA in young women (see Table S2). In addition, the risk of APO-induced EVA remained significant after limiting the study population to women who had a single delivery (Table S3) or excluding women with chronic hypertension or diabetes mellitus (Table S4).
Although we observed that APOs were a risk factor for EVA in young women, we were unable to elucidate the mechanism because this was an observational study. Possible mechanisms based on previous studies and our own data are : stress test in pregnancy caused by APOs that do not stop after delivery, such as inflammatory response [38], postpartum metabolic abnormalities, sympathetic nerve excitation, and elevated soluble vascular endothelial growth factor to placental growth factor ratio [39]. In addition, the risk factors for APOs, including low socioeconomic level, prepregnancy overweight, hypertension, and abnormal glucose and lipid metabolism, are also risk factors for EVA.
Strengths: 1. APOs were diagnosed based on medical records rather than recall in this study, which yielded more accurate data. Stuart et al. [40] confirmed that the sensitivity of recalled APO history was low. EVA is the result of direct vascular damage caused by various risk factors, including APOs, and is more direct and reliable than evaluations of other risk factors. 2. This study used baPWV, a non-invasive, inexpensive and clinically convenient measure that correlates well with carotid-femoral pulse-wave velocity (cfPWV), as a measure of EVA. 3. The population of this study was young women, which was not conducive to the analysis of the effect of APOs on ASCVD but beneficial to analyze the effect of APOs on EVA.
Limitations: 1. This study lacked prepregnancy baPWV data; therefore, we could not determine whether APOs were the cause of EVA. 2. This study did not include placental abruption and stillbirth. 3. This study did not include the type of exercise. 4. This study did not use 24-hour urinary sodium excretion to estimate daily salt intake, but we randomly selected 231 people from the Kailuan cohort to conduct a confirmatory study. The results revealed a significant dose–response relationship between self-reported salt intake and estimated 24-hour urinary sodium excretion [41]. Previous studies have also found that self-reported salt intake can predict actual salt intake [42].
Conclusion
Adverse pregnancy outcomes have a substantial impact on the risk of early vascular aging and early vascular aging should be an important indicator for preventive cardiovascular risk management in young women.