Focused on rural population, this large cross-sectional study is the first research which aimed to explore the association between different blood pressure proxies and osteoporosis, and to detect the potential gender-difference. In rural China, the prevalence of osteoporosis was 14.07% for men and 22.64% for women and the significantly positive association between hypertension and osteoporosis was observed in women but not in men. Each 10 mmHg increase in SBP and PP corresponded with 1.07-fold (1.03,1.12) and 1.08-fold (1.02,1.15) risk for prevalent osteoporosis among women, respectively. This positive association was still significant among non-hypertension women and postmenopausal women, but not exist among pre-menopausal women and men, which hinted that the gender-difference association between blood pressure and osteoporosis may attribute to the menopause status.
The prevalence of osteoporosis in China varied across researches, but it is consistent that women were more prone to suffer osteoporosis in all researches . For instance, a Chinese research completed in northern China reported that the prevalence of osteoporosis was 19.8% among elderly men and 36.9% among elderly women. While in northwestern China, the reported prevalence of osteoporosis was 8.08% among elderly men and 9.65% among elderly women . One nationwide research reported that the prevalence of osteoporosis was 6.46% among men and 29.13% among women . Another nationwide research reported that the prevalence of osteoporosis was 13.5% for men and 29.0% for women . While in this research, the prevalence of osteoporosis was 14.07% for men and 22.64% for women in Chinese rural areas. The difference in prevalence of osteoporosis may be attributed to the different measurements of BMD across researches.
Numerous researches have repeatedly linked hypertension with prevalent osteoporosis . Early cohort study conducted in 3676 elderly white women found increasing SBP corresponded with increasing rate of bone loss (Pnon−linear <0.05) , which was similar to our results. Recent cross-section study also indicated that both SBP and DBP were inversely related with BMD of proximal femoral and lumbar vertebral, the betas were − 0.382, -0.290 and − 0.340 of SBP, and − 0.318, -0.340, and − 0.304 of DBP . Similar association was also observed in Chinese population [24–25]. Conducted in Tibet, a retrospective cross-sectional study also found SBP was inversely associated with BMD T-score of spine and femoral neck or hip among diabetic postmenopausal women . Recent case-control study also indicated that hypertension was positively associated with osteoporosis . In contract to our results, Javed et al. reported that hypertension was not correlated with low BMD at either lumbar spine or both femoral necks among African American females aged over 65 years . A retrospective analysis also pronounced that there was no significant difference between hypertension and non-hypertension participants in BMD of femur or spinal . Evidence from Korea National Health and Nutrition indicated that lumbar spine osteoporosis was not significantly associated with blood pressure . A population-based Mendelian randomization study conducted in European population also revealed a potential positive association between PP and forearm BMD . These differences may be the results of different regions, environment exposures, lifestyles, races and other underlying factors.
Gender-difference association between blood pressure with osteoporosis was repeatedly observed in previous researches. For instance, Loke et al. observed that both SBP and DBP were negatively associated with BMD among women, but not significantly associated among Men . A recent longitudinal study also highlighted that BMD of femoral neck was lower in women with hypertension than those without hypertension (0.80 vs. 0.82), while in men, hypertension was positive associated with BMD of lumbar spine and femoral neck . Additionally, evidence from a meta-analysis pronounced that the association between fracture and hypertension was slightly stronger in women (pooled OR = 1.52, 95% CI 1.30–1.79) than in men (pooled OR = 1.35, 95% CI 1.26–1.44) . Given the positive association between blood pressure and osteoporosis was disappeared in pre-menopausal women, the gender-difference association may be attributed to the menopause status. Additionally, lower sample size in men may also contribute to this statistical insignificance.
Despite the potential mechanism of blood pressure and osteoporosis was not yet clarified, limited researches still provided various evidence. Calcium may be a primarily bridge between blood pressure and osteoporosis . Previous researches have reported that participants with hypertension had a higher calcium elimination and a lower intestinal absorption than non-hypertension participants, which contributed to a lower calcium concentration in the plasma [13, 31–32]. To sustain a suitable blood calcium level, bones may breakdown and bring calcium into the blood . Therefore, bone may be porous and prone to fractures [31, 34–35]. In addition, recent research also found hypertension corresponded with the low level of 25-hydroxy vitamin D and osteocalcin, which leaded to a low bone turnover . During menopause and postmenopause, the reduced estrogen in women would contribute to an increased osteoclastic resorption activity without a suitable increase in osteoblastic activity, which lead to a net loss of bone and a decreased bone strength [36–38]. Thus, the low bone strength of may explain the significant association between blood pressure and osteoporosis was only observed among postmenopausal women but not among men or pre-menopausal women.
To the best of our knowledge, this is the first research to explore the gender-difference associations between divergent blood pressure proxies and osteoporosis among rural population. Despite large sample population and appropriate statistical methods could make this research more convincing, some limitations should be noted. Firstly, only 7689 participants from Henan Rural Cohort study were included in this research and missing information may induce inevitable errors. Secondly, quantitative ultrasound (QUS) measures might underestimate osteoporosis prevalence, however, it appeared capable of replacing dual X-ray considering its portability and low-cost in the large-scale study. Thirdly, we did not examine vitamin D, osteoprotegerin, osteocalcin levels of the subjects. These metabolic makers might help to enrich our results. Fourthly, lack of the information of anti-hypertensive drags would weaken the results. Moreover, the unraveling reverse causality cannot be ruled out because of the survey based on a cross-sectional study.
In conclusion, hypertension and high blood pressure were positive associated with prevalent osteoporosis among women in rural areas. This positive association was still significant in non-hypertension women but not in pre-menopausal women, which hinted that this gender-difference association may be attributed to menopause status. These findings might hopefully identify that divergent blood pressure proxies may be the potential indicators for screening high osteoporosis risk among women in rural areas with limited medical resource. And more attention should be attention to the postmenopause women with high blood pressure.