沈阳地区人群5254例骨密度调查研究

目的 调查沈阳地区部分人群骨密度，为骨密度正常参考值数据提供资料，为沈阳乃至全国骨质疏松预防、诊断、治疗提供科学依据。方法 应用双能X线骨密度检测仪对沈阳各区县部分人群5254例进行骨密度检测，以分析软件进行统计、比较。结果 统计出各年龄组骨密度，计算骨密度丢失率及患病率，比较城乡及不同职业间骨密度差异。结论 沈阳地区男女骨密度峰值均在26-30岁年龄组，女性50岁、男性60岁以后骨密度丢失率、患病率升高，女性66-70岁年龄骨密度均值城乡有显著差异。     

辛伐他汀对桡骨远端骨折老年女性骨密度及骨折愈合的影响

目的探讨辛伐他汀对老年女性桡骨远端骨折骨密度及骨折愈合的影响。方法分析98名桡骨远端骨折老年女性术前及术后3个月健侧桡骨远端1/3处骨密度,依据术后是否口服辛伐他汀治疗其他内科疾患分为辛伐他汀治疗组(56例)及对照组(42例)。结果治疗前辛伐他汀组与对照组健侧桡骨远端1/3处骨密度差异无统计学意义(P0.05)。治疗3个月后辛伐他汀组健侧桡骨远端1/3处骨密度与治疗前骨密度相比差异具有统计学意义(P0.05);对照组健侧桡骨远端1/3处骨密度均值增高,与初始时差异无统计学意义(P0.05)。治疗3个月后辛伐他汀组与对照组两组间骨密度差异无统计学意义(P0.05)。通过卡方检验分析发现辛伐他汀组与对照组相比骨折愈合数存在统计学差异,辛伐他汀可以促进骨折愈合;分析两组间治疗前后骨质正常、骨量减少、骨质疏松数之间差异无统计学意义,辛伐他汀不影响骨质疏松患病率。结论桡骨远端骨折老年女性应用辛伐他汀(20 mg/d)可以改善桡骨远端骨密度、促进骨折愈合,但不影响骨质疏松患病率。     

骨密度对骨质疏松性骨折的判断价值

目的研究骨密度对骨质疏松性骨折的判断价值。方法共3组研究对象,398例骨质疏松不伴有骨折的研究对象(A组),胸腰椎骨折患者(B组),骨密度正常的正常组进行研究。研究骨密度的一般情况、不同T值在各组的分配情况,骨质疏松性骨折与骨密度(BMD)的相关性。结果腰椎L2-L4、L2-L4和股颈的BMD值之间,T值人数分配之间,正常组、A组以及B组的差别具有统计学意义(P<0.05)。腰椎L1-L4、L2-L4和股颈的BMD以及总BMD的测定值均与骨质疏松性骨折相关。结论我们认为:本地区所收治的骨质疏松性骨折患者,全部应诊断判定为骨质疏松症。     

福善美对绝经后妇女骨密度的影响

目的　评价福善美 (Fosamax)治疗绝经后骨质疏松症妇女的近期及中期疗效 ,以及改善骨量作用。方法　绝经 1年以上女性 80名 ,分成 4组 ,A组 :14例 ,年龄 5 4 . 97± 5. 5 1(47～ 6 2 )岁 ,绝经年限≤10年 ,疗程 6个月～ 1年 ;B组 :2 3例 ,年龄 5 5 . 5 5± 3. 6 6 (5 0～ 6 2岁 ) ,绝经年限≤ 10年 ,疗程 1年以上 ;C组 :18例 ,年龄 6 8. 18± 5 . 5 9(5 9～ 78岁 ) ,绝经年限 >10年 ,疗程 6个月～ 1年 ;D组 :2 5例 ,年龄6 7. 2 5± 6 .19(5 2～ 80岁 ,绝经年限 >10年 ,疗程 1年以上。患者每天接受口服福善美 10mg和元素钙5 0 0mg,疗程 6个月～ 2 8年。治疗前、后应用双能X线吸收仪 (HologicQDR 2 0 0 0型 )进行骨密度(BMD)测定。结果　 4组不论绝经年限长短 ,通过 6个月～ 2年以上福善美治疗 ,腰椎BMD平均增加百分率 3 74 %～ 5 4 5 % ,较基础值均有明显增加 (P <0 . 0 0 1) ,4组间差异无统计学意义 (P >0 . 0 5 )。股骨颈部位治疗后BMD平均增加百分率为 0 84 %～ 4 2 1% ,其中绝经年限相同时 ,疗程长者高于短者 ,即B组高于A组 ,D组高于C组 ;疗程相同时 ,绝经年限长者高于短者 ,即C组高于A组 ,D组高于B组 ,但 4组间差异无显著性 (P >0 . 0 5 )。大转子部位治疗后BMD增加平均变化百分率 1 4. 2 %～     

跟骨超声骨质测量与双能量X线吸收骨密度测量的比较

我们试图通过对跟骨超声骨质测量仪与双能量Ｘ线吸收骨密度测量仪的临床对比，来评价跟骨超声骨质测量仪的敏感性。本文对５６名健康女性同时接受了超声骨质测量仪和双能量Ｘ线吸收骨密度仪的检测。３７例（年龄２６～７６岁）进行了跟骨超声和腰椎骨密度测量，１９例（年龄２６～７０岁）进行了跟骨超声和股骨颈骨密度测量。结果用ＳＹＳＴＡＴ统计软件包进行处理。结果表明：随着年龄的增加，腰椎、股骨颈骨密度及跟骨强度（Ｓｔｉｆｆｎｅｓｓ）均显著下降（Ｐ＜０．０５），两种仪器的阳性检出率无明显差异（Ｐ＜０．０５）。但腰椎和股骨颈ＢＭＤ与跟骨强度（Ｓｔｉｆｆｎｅｓｓ）的相关性适中ｒ＝０．４６５～０．５１３左右。通过逐步多元回归分析显示超声强度（Ｓｔｉｆｆｎｅｓｓ）与ＢＭＤ无关。这表明超声波测量仪主要测量骨的结构变化，而骨密度测量仪则是测量骨量的变化。两种方法相辅相承，共同测量，将更好地预测骨质疏松性骨折的发生。同时超声波具有无放射线损害、价格低廉及良好的敏感性，将越来越受到临床重视。     

Subregion analysis of the rat femur: A sensitive indicator of changes in bone density following treatment with thyroid hormone or bisphosphonates

Measurement of bone mineral density (BMD) by dual X-ray absorptiometry (DXA) is a precise and accurate way to assess changes in BMD due to a variety of causes. However, the degree of bone loss may vary depending on the skeletal site examined. We postulated that interventions that change bone density would have a different effect on an area rich in trabecular bone, such as the distal femur, than on other subregions of the femur. Male Sprague-Dawley rats (325–350 g) were treated with triiodothyronine (T₃), a bisphosphonate (pamidronate), or placebo for 21 days and then sacrificed. Ex vivo BMD of the proximal, distal, mid and total femur were measured by DXA. We found that mean BMD of hyperthyroid rats was significantly lower than controls at all femoral subregions. However, the difference in mean BMD between hyperthyroid and control rats was greatest at the distal femur (8.6%). In rats treated with bisphosphonate, mean BMD was significantly higher than controls at the proximal, distal, and total femur. The difference in mean BMD between controls and rats treated with bisphosphonate was greatest at the distal femur (31.8%). Furthermore, pamidronate (APD)-treated rats had lower mean mid-femur BMD than controls. We conclude that changes in BMD after treatment with bisphosphonate or T₃ are greatest at the distal femur subregion, and that treatment with bisphosphonate may cause a slight reduction in midfemur BMD. Future studies examining changes in BMD in the rat femur after interventions that alter mineral metabolism should include subregion analysis.Portions of the data presented here were presented at the Fourteenth Annual Meeting of the American Society for Bone and Mineral Research, Minneapolis, Minnesota, September 30–October 4, 1992.     

漯河地区中老年骨质疏松性骨折与股骨近端骨密度相关性研究

目的 调查漯河地区中老年骨密度(BMD)的变化规律和骨折之间的关系。方法 采用法国Medlink公司的的双能X线骨密度仪对漯河地区649名中老年人进行健侧髋部股骨颈、大转子、粗隆间和全髋的骨密度值测量。结果 骨折组各年龄段、各部位的BMD均比非骨折组低（P<0.05）。随着年龄的增长股骨近端骨量逐渐丢失,除了45~组,其余区域各年龄段骨折组的患病率明显高于非骨折组(P<0.05),骨密度值越低,骨折危险性越大。结论 中老年人骨近端骨密度值与发生骨质疏松性骨折之间存在密切关系,不容忽视。     

Characteristics of regional bone mineral density and soft tissue composition in patients with atraumatic vertebral fractures

To clarify the characteristics of total body and regional bone mineral density (BMD) and soft tissue composition in patients with atraumatic vertebral fractures (AVF), we measured total body and regional BMD, lean mass, and fat mass using dual-energy X-ray absorptiometry. Sixty-four women, aged 55–75 years, were divided into two groups: women with AVF (fracture group, n = 30) and women without AVF (nonfracture group, n = 34). Mean BMD of the second to fourth lumbar vertebrae (L2–4BMD), regional BMD, and soft tissue mass were measured. Regional BMD was measured in the head, arms, legs, ribs, thoracic vertebrae, lumbar vertebrae, and pelvis. Lean mass and fat mass of head, arms, legs, and trunk were measured. L2–4BMD, total body BMD, and BMD of the lumbar spine, thoracic spine, and pelvis of the fracture group were significantly lower than those of the nonfracture group (P < 0.001). Total lean and fat mass of the fracture group tended to be lower than that of the nonfracture group. The results suggest that BMD of weight-bearing bones, except for that of the bones of the legs of the fracture group, is significantly lower than that of the nonfracture group, and that total body lean and fat mass may be a predictor for AVF. Received: September 27, 1999 / Accepted: January 7, 2000     

Bone mineral density predicts osteoporotic fractures in elderly men: the MINOS study

Osteoporosis in men is becoming a public health problem in developed countries. Fracture incidence increases with age, and the number of fractures increases because of the ageing of the population. We assessed the predictive value of bone mineral density (BMD) for osteoporotic fractures evaluated prospectively in a large cohort of elderly men and assessed the sensitivity of the T-score =–2 to detect men who will sustain a fracture. Fracture incidence was evaluated for 90 months in 759 men from the MINOS cohort aged 50 and over at baseline. In 74 men, 77 incident vertebral and peripheral fractures occurred. BMD was measured at baseline at the lumbar spine, hip, whole body and distal forearm. The incidence of osteoporotic fractures increased with age and with decreasing body weight. In men with low BMD (T-score <–2), fracture incidence varied from 2.26 to 3.07 fractures per 100 person-years and was 2.1 to 3.6 times higher than in men with normal BMD. After adjustment for age, body weight and height, baseline BMD was 3.7 to 7.9% ( P <0.05–0.0001) lower at all the sites of measurement in men who sustained a fracture. After adjustment for age, weight and prevalent fractures, BMD was predictive of osteoporotic fractures at all the sites. Odds ratios varied from 1.28 to 1.89 per 1 SD decrease in BMD ( P <0.05–0.0001). The predictive accuracy of BMD for fractures (area under the curve of the receiving operator characteristics adjusted for age, weight and prevalent fractures) varied from 0.643 to 0.712 according to the skeletal site and was higher for the whole body than for other sites. Thus, BMD itself has a limited value for determining men at an increased risk for fracture. The percentage of incident fractures occurring in men with low BMD (T-score <–2) ranged from 13.7% at the trochanter to 44.6% at the ultradistal radius. Conversely, 27 to 45% of incident fractures occurred in men with mildly decreased BMD (T-score between –1 and –2). In conclusion, BMD predicts osteoporotic fractures in men independently of age, body weight and prevalent fractures. However, the sensitivity of BMD to detect men at high risk of fracture is low. More studies on the predictors of fractures in men, such as bone architecture, morphology, biochemical markers of bone turnover and hormonal levels, are necessary.     

Physical training preserves bone mineral density in postmenopausal women with forearm fractures and low bone mineral density

Summary One hundred and twelve postmenopausal women with low bone mineral density (BMD) and forearm fractures were randomized to physical training or control group. After one year the total hip BMD was significantly higher in the women in the physical training group. The results indicate a positive effect of physical training on BMD in postmenopausal women with low BMD. Introduction The fivefold increase in hip fracture incidence since 1950 in Sweden may partially be due to an increasingly sedentary lifestyle. Our hypothesis was that physical training can prevent bone loss in postmenopausal women. Methods One hundred and twelve postmenopausal women 45 to 65 years with forearm fractures and T-scores from −1.0 to −3.0 were randomized to either a physical training or control group. Training included three fast 30-minute walks and two sessions of one-hour training per week. Bone mineral density (BMD) was measured in the hip and the lumbar spine at baseline and after one year. Results A per protocol analysis was performed, including 48 subjects in the training group and 44 subjects in the control group. The total hip BMD increased in the training group +0.005 g/cm2 (±0.018), +0.58%, while it decreased −0.003 g/cm2 (±0.019), −0.36%, (p = 0.041) in the control group. No significant effects of physical training were seen in the lumbar spine. A sensitivity intention to treat analysis, including all randomized subjects, showed no significant effect of physical training on BMD at any site. Conclusions The results indicate a small but positive effect of physical exercise on hip BMD in postmenopausal women with low BMD.     

大连青年腰椎和股骨近端骨密度的调查

目的探讨大连地区青年骨密度现状及运动对骨密度的影响,为骨质疏松预防提供科学依据。方法采用双能X线吸收法,测量了大连市内486名(男性266,女性220)健康汉族青年的第2~4腰椎椎体、股骨颈、Ward三角和大转子的骨密度,并测量其身高和体重。结果(1)大连青年第2~4腰椎椎体、股骨颈、Ward三角和大转子的骨密度男性分别为1.107、1.028、0.901和0.883,女性分别为0.978、0.963、0.859和0.847,男性明显大于女性并差异有显著性(P<0.05)。(2)大连男女青年中经常参加运动的骨密度比不参加运动的骨密度高,并差异有显著性(P<0.05)。(3)大连男女青年的骨密度总体低于内陆地区,高于南方地区。(4)大连男女青年身高、体重及体重指数与骨密度呈正相关。结论大连青年骨密度处中下水平,骨密度有明显的性差,运动有利于增加骨密度。     

骨质疏松性骨折与骨密度关系的研究进展

骨质疏松症是老年人的常见病和多发病,其最大的危害是导致骨折的发生。随着老年人口的增加,骨质疏松性骨折的发病率也显著增高,这已经引起了医学研究者的普遍关注。近年来对运用骨密度检测来预测骨质疏松性骨折的研究很多,但是还没有形成一个定论,故对运用骨密度检测来预测骨质疏松性骨折的研究现状作一简单综述。     

微动对骨折端骨密度的影响

目的:研究骨折端微动时应力对骨密度的影响。方法:60只新西兰大白兔随机分为微动组与固定组,每组30只。固定组术后使骨折端固定。微动组使外固定架中间杆有0.5mm的轴向移动,术后动物自由行走,依靠体重使外固定架产生微动。利用双能X线骨密度测量仪测定两组动物骨痂的骨密度。结果:术后14d时固定组、微动组骨密度为正常的10%左右,两组无显著差异。21、28d两组骨密度有明显上升,微动组与固定组比较差异有显著性意义(P<0.01)。42d时微动组骨密度高于正常水平。56d时微动组骨密度稍下降,但仍高于正常,固定组骨密度高于正常水平,两组无显著差异(P>0.05)。结论:微动可增强骨愈合时骨痂的骨密度。     

骨折病人的骨密度检测

目的 观察骨折病人骨折治疗前后的骨密度变化.方法对202例男性骨折病人和96例女性骨折病人在骨折后1w、1个月、3个月、6个月时进行数字X线骨密度测量(XBM),观察骨密度值的变化.结果 男、女骨折病人骨折后1个月时与骨折时比较,男:降低4.84%;配对t检验:t=6.134,P<0.001;女:降低5.71%;t=4.734,P<0.001;3个月时与骨折时比较,男:降低1.41%;配对t检验:t= 1.288,P>0.05;女:降低2.10%;t=1571,P>0.05;6个月时与骨折时比较,男:降低0.26%;配对t检验:t= 0.009,P>0.05;女:降低0.60%;t=0.288,P>0.05.结论 男、女骨折病人骨折后1个月时有非常显著的骨密度降低,3个月时骨密度有明显恢复,较骨折时已无显著性降低;6个月时基本恢复到接近正常水平,与骨折时比较没有显著性差异.     

绝经后女性骨质疏松性椎体骨折与腰椎体骨密度的相关性

随着我国步入老龄化社会,骨质疏松症的患病率明显升高。骨质疏松症最严重的危害来自骨质疏松性骨折,绝经后女性尤其多见。由于脊柱独特的解剖学和生物力学特点,骨质疏松患者更易发生椎体骨折。骨密度测量是诊断骨质疏松的金标准。本文通过回顾近年来相关文献,探讨腰椎体骨密度检测对绝经后女性骨质疏松性椎体骨折的意义,发现:绝经后骨质疏松性椎体骨折患者的BMD水平比绝经后骨质疏松症但无脊椎骨折者明显减少;绝经后骨质疏松症患者的BMD水平越低,其发生椎体骨折的风险越高;有椎体骨折史的绝经后骨质疏松症患者的BMD水平与发生再次椎体骨折的风险呈负相关。药物干预通常可明显提高绝经后骨质疏松症患者的BMD水平,同时还可减少椎体骨折的发生。尚存在一些不足:腰椎骨密度可能出现假性增高;需进一步探讨预测骨质疏松性椎体骨折的骨密度阈值;药物干预的研究中BMD水平与椎体骨折发生的相关性并没有得到深入研究;缺少大规模的绝经后骨质疏松性椎体骨折的流行病学,现有研究也大都存在病例收集方法不规范、样本量小、年龄分布存在差异等不足。对绝经后骨质疏松性椎体骨折的深入研究需要多学科共同协作。     

环磷酰胺对大鼠骨密度和骨微结构的影响

目的：研究不同剂量环磷酰胺对雌性SD大鼠骨密度和骨微结构的影响。方法40只3月龄SD雌性大鼠随机数字表法分为环磷酰胺低剂量组、中剂量组、高剂量组和对照组,每组各10只,环磷酰胺各组分别腹腔注射不同剂量（5 mg／kg、8 mg／kg、10 mg／kg）的环磷酰胺,对照组腹腔注射等量生理盐水,每天一次,连续15天,观察大鼠骨密度及骨微结构等指标。结果不同剂量的环磷酰胺组与对照组比较,全身骨密度分别下降了9．8％、13．3％和15．6％;股骨骨小梁数目分别下降了49．8％、65．5％和72．8％;股骨骨小梁分离度则分别上升了225．2％、416．9％和577．4％。结论环磷酰胺可使大鼠骨密度降低,骨小梁数量减少,骨微结构受损,且环磷酰胺剂量越大,骨微结构受损越严重。     

Changes in bone mineral density after allogenic stem cell transplantation

ObjectiveOsteoporosis is a complication after allogenic stem cell transplantation (alloSCT). The purpose of this study was to assess changes in bone mineral density (BMD) 6 months and 3 years after alloSCT, as well as predictors of bone loss.MethodsA longitudinal, prospective, single-center study was conducted at Lille University Hospital between 2005 and 2016. Clinical, biological, radiologic (thoracic and lumbar spine) and densitometric (DXA) assessments were carried out at baseline (pre-transplant), 6 months and 3 years. Patients with myeloma were not included.ResultsTwo hundred and fifty-eight patients were included (144 men). Among them, 60.1% had leukemia and 65.8% of them, acute myeloid leukemia. At baseline, 6 months and 3 years, DXA-confirmed that osteoporosis was observed in 17%, 22.8% and 17.5% of the patients, respectively, mainly at the femoral neck. At baseline, 6 months and 3 years, 9 (8.5%), 53 (21.5%) and 38 (16.7%) patients, respectively, were receiving anti-osteoporotic treatment. From baseline to 6-month follow-up, BMD decreased significantly (p < 0.001) at the lumbar spine (?36 [95%CI; ?51 to ?20] mg/cm² of hydroxyapatite), femoral neck (?43 [95%CI; ?57 to ?29] mg/cm² of hydroxyapatite) and total hip (?53 [95%CI; ?68 to ?39] mg/cm² of hydroxyapatite). From 6-month to 3-year follow-up, a significant increase in BMD was observed at the lumbar spine only (+31 [95%CI; 20 to 42] mg/cm² of hydroxyapatite, p < 0.001). At all 3 sites, changes in BMD did not differ between patients treated or untreated by anti-osteoporotic treatment from 6-month to 3 year follow-up. Incident fractures were found in 4.1% and 5.7% of the patients at 6 months and 3 years, respectively. Between baseline and 6 months, bone loss at all 3 sites was associated with corticosteroid intake. At the total hip, 23.3% of the decrease in BMD from baseline to 6 months was due to an active hematological disease (p < 0.05), a bone marrow stem cells (p < 0.01) and a corticosteroid intake (p < 0.01).ConclusionOur study found evidence of bone fragility in alloSCT patients. Low BMD persisted at the hip 3 years after transplantation due to slower improvement at this site.     

牙齿缺失与骨密度关系的研究

目的系统骨丢失与牙槽骨局部骨丢失致牙齿缺失之间的关系尚不清楚，通过检测健康藏族妇女的骨密度及其牙齿缺失状态，探讨其相关性。方法随机选择西藏拉萨40—79岁健康藏族妇女(无牙周疾病治疗史)135人，检查牙齿缺失状况确定缺牙原因。问卷调查排除系统病和服用影响骨密度和钙磷代谢药物史。同时用MetriScan TM(美国Alara公司提供)指骨骨密度仪进行骨密度测量，应用SPSS软件统计分析。结果随年龄增长，因牙周病而缺牙的人占同年龄人数的百分率逐渐升高，骨密度逐渐降低。结论骨质疏松症是牙周病的危险因子之一。     

甲状腺功能异常患者血生化、骨代谢及骨密度特点的临床研究

目的观察甲状腺功能减退症及甲状腺功能亢进症对骨密度以及骨代谢相关指标的影响。方法纳入甲状腺功能减退症女性37例为甲减组,甲状腺功能亢进症女性41例为甲亢组,健康体检女性人员40例为对照组。观察3组甲状腺功能指标血游离三碘甲状腺原氨酸(FT_3)、游离甲状腺激素(FT_4)和高敏感促甲状腺激素(TSH);骨代谢指标血Ca~(2+)、血P~(3+)、1,25-(OH)_2D_3、甲状旁腺激素(PTH)、碱性磷酸酶(ALP)、血清Ⅰ型胶原羧基端吡啶并啉交联肽(ICTP)以及血清骨钙蛋白(BGP)以及左侧股骨颈、正位腰椎1-4(L_(1-4))的骨密度情况。结果甲亢组血清FT_3、FT_4、ALP、BGP、ICTP水平高于对照组(P0.05),甲亢组血清TSH水平低于对照组(P0.05)。甲减组血清TSH水平高于对照组(P0.05),而血清FT_3、FT_4、ALP、BGP、ICTP水平显著低于对照组(P0.05)。甲亢及甲减组L1-4及左股骨颈骨密度显著低于对照组(P0.05)。3组受试者PTH、CT、Ca~(2+)、P~(3+)、1,25-(OH)_2D_3比较无统计学意义(P0.05)。结论甲亢及甲减都可以引起骨量丢失,骨密度降低;主要通过影响骨转化来实现的;应该重视甲状腺功能异常引起的骨密度及骨代谢异常。     

Familial aggregation of bone mineral density and bone mineral content in a Chinese population

Familial aggregation of bone mineral density (BMD) and bone mineral content (BMC) has been shown in twin and familial studies, but most sample sizes were small. We here report a large familial aggregation study in a Chinese population. A total of 13,973 siblings aged 25–64 years from 3,882 families were enrolled from Anhui, China. We assessed the whole-body, hip and lumbar spine BMD and BMC by dual-energy X-ray absorptiometry (DXA). Intra-class correlation coefficients of BMD and BMC between siblings varied among different skeletal sites and between different age groups of male sib-pairs and premenopausal and postmenopausal female sib-pairs, with a range of 0.228 to 0.397. The sibling recurrence risk ratio (s) of osteoporosis was 2.6 in our population. We also evaluated the joint association of the BMD values of the first siblings and the second siblings with the risk of low BMD (defined as less than the 10th percentile of the same group population) of their younger siblings. If both the first and second siblings BMDs were in the lowest tertile, the odd ratios (ORs) of low BMD in their subsequent siblings were 8.32 [95% confidence interval (CI) 5.59–12.39)], 8.71 (95% CI 5.74–13.22) and 5.90 (95% CI 3.57–9.76) for total body, total hip and lumbar spine, respectively. This study demonstrates a significant familial aggregation of BMD and BMC in a large sample of rural Chinese adults.