Abstract and Introduction
Abstract
Osteoporosis is a serious national and global public health problem, but data on bone health are limited for Asian women living in the U.S., the majority of whom are Chinese. For this study, we measured bone mineral density (BMD) by dual energy X-ray densitometry (DXA) at the lumbar spine and hip region in 300 immigrant Chinese women, ages 40-90 y, living in New York City. We also collected demographic and health data, information about knowledge and care for osteoporosis, and anthropometric measures, and estimated calcium intake from the women. In our sample, 55% had osteoporosis and 38% had low bone mass (osteopenia). Older age, lower body mass index (BMI), and shorter height were associated with lower BMD at all sites. Years lived in the U.S. and number of children were also associated with lower BMD of the lumbar spine. Chinese women who emigrated from Mainland China had lower BMD at the lumbar spine and femoral neck than Chinese women who emigrated from Hong Kong, after adjusting for potential confounders. Both groups of immigrant women had lower BMD at all sites than a national sample of U.S. Caucasian women. Although the women in our study had generally poor knowledge about osteoporosis, most could identify at least one food rich in calcium. The large number of immigrant Chinese women in New York City with osteoporosis calls for major efforts to increase awareness, prevention, diagnosis, and treatment of this condition in this susceptible population.
Introduction
Osteoporosis affects 10 million Americans and many more millions of people globally. More than 1.5 million fractures, including 300,000 hip fractures and 700,000 vertebral fractures, are attributed to osteoporosis annually in the U.S. One-fourth of adults over age 50 with hip fractures are estimated to die within a year of the fracture, due mostly to chronic illnesses that preceded the fracture. Adults with vertebral fractures also have increased risk of mortality beyond the first year, due to both the direct effects of the fracture and to underlying health conditions. In 2001, the estimated national direct expenditures for osteoporosis and fractures was $17 billion. This amount will only increase as the U.S. population ages. Clearly, a major public health effort is needed to prevent and to treat this disease. However, these data are based primarily from Caucasian Americans; little is known about bone health and osteoporosis of other groups such as Asian Americans, particularly those who immigrate to the U.S.
According to national census data, the U.S., and particularly New York City, has experienced rapid growth in its Asian immigrant population during the past decade. In 2000, Asian Americans comprised 4.2% (11.9 million) of the U.S. population and 25.5% of the foreign-born population, and are expected to increase to 8.0% (33.4 million) of the U.S. population by 2050. Approximately 2.7 million identified themselves as Chinese, comprising the leading Asian group. Over half (51%) of the Asian population lived in New York, California, and Hawaii; almost half (45%) of the Asian-born population lived in New York City, Los Angeles, and San Francisco.
Although data suggest that Chinese women may improve their BMD when they immigrate to westernized countries, most studies have reported data on BMD of women living in Hong Kong and Mainland China, and compared their findings to BMD of U.S. Caucasian women. In general, Hong Kong and Mainland Chinese women have lower BMD than U.S. Caucasian women, but these differences diminish when body size is considered. In the U.S., data from the Study of Women's Health Across the Nation (SWAN), a large multiethnic community-based study, showed that Chinese women had higher BMD than Caucasian women when body weights were comparable. However, a recent study of older immigrant Chinese women living in Chicago reported lower average BMD than reference data for Caucasian women and U.S.-born Asian Americans, and concluded that foreign-born Chinese women are a high-risk group for osteoporosis. The objectives of this study were to measure the BMD of the lumbar spine and hip region in immigrant Chinese women living in New York City, and to determine whether differences exist between the women born in Hong Kong and the women born in Mainland China compared with published data from Chinese women and national data from U.S. Caucasian women. We also wanted to assess the women's knowledge about osteoporosis and related care.