Hip fracture is increasingly becoming a major health problem in India and knowledge about risk factors is essential for its prevention. Although many large scale studies have been reported in White and Asian (other than Indian) populations, there is currently no research available on variables that increase the risk of hip fracture in the Indian population. This pilot case control study revealed many vital risk factors for an urban Indian population. This section outlines the results of the study in the context of previous research, and indicates certain limitations of this study that should be focused on in future research.
Risk factors were assessed by interview through a standardized questionnaire. This analysis focused on identifying risk factors for hip fracture in the univariate and multivariate setting. A number of risk factors that were significant in the univariate analysis were not included in the final model produced by the stepwise selection routine. This is anticipated as the correlation between the risk factors may reduce their relative importance. In addition, effect modification may be present amongst the risk factors based on a comparison of odds ratios yielded by the univariate and multivariate models. For example, the effect of tea consumption is significantly elevated in the multivariate model. This suggests that the effect of tea consumption is modified by the presence of another risk factor in the multivariate model. Future investigations may include an in-depth analysis of interactions.
We found that dietary calcium, vitamin D, increased BMI, and higher activity levels have a protective effect on hip fractures. On the other hand caffeine intake (as measured by tea intake) and decreased agility increase the risk of hip fracture. Our results are largely in agreement with the studies conducted in White and Asian populations. In the Mediterranean osteoporosis study conducted in Europe, Johnell et al. found that late menarche, poor mental function, low BMI, lack of physical activity, low exposure to sunlight, and low consumption of calcium and tea to be significantly associated with the risk of hip fracture. In the Asian osteoporosis study, Lau et al. found low dietary calcium intake, lack of physical activity, alcoholism and cigarette smoking to be risk factors for hip fracture. Similarly, in Japan, Fujiwara et al found a low BMI, regular alcohol intake, prevalent vertebral fracture, having 5 or more children, a low milk intake and later age at menarche to be associated with risk of hip fracture.
Unlike the American and European population where the prevalence of hip fractures in women is more than twice that of men in any age group, the ratio in the Indian population appears to be 58% to 42%. Future research could explore this discrepancy. One possible reason could be the disparity in life expectancies in the different populations. The 2003 life expectancy at birth was 61.8 years for Indian males and 63.5 years for Indian females . However the life expectancy at birth was 75.2 years for American males and 80.4 years for American females . Thus not only are the life expectancies of Indians more balanced with regards to sex relative to the Americans, but the values are also significantly lower than their western counterparts.
Consistent with previous research [4, 7, 16, 17], men and women with a lower BMI are at a significantly higher risk for hip fracture than their heavier counterparts. It has been suggested by these prior studies that this protection is a result of increased adipose tissue based production of estrogen, more padding around the hips that may decrease the energy transmission from the impact of the fall to the proximal femur, and the greater gravitational forces on bone mass[16, 18]. However, this study did not examine the body distribution of adipose tissue. In American and European people, hip fracture risk increases with body height. However we did not find a significant association between risk of hip fracture and height.
Although not found significant in another research study our data suggest that difficulty in getting up from a chair significantly raises the risk of hip fracture. It could be a risk factor for falls, but it could also be an important proxy for agility. More studies are required to determine the significance of this variable.
In accordance with previous research, physical activity greatly reduces the risk of hip fracture [12, 16, 19]. It is important however to quantify the load-bearing activity to determine its effect on bone mineral density.
Dietary calcium has been determined to be crucial in reducing the risk of hip fracture not only in this pilot study but also in other Asian studies involving the Chinese, Malaysian, Singaporean, Thai and Philippino populations[12, 20]. A European study has shown that the risk of hip fracture increases with diminishing calcium intake in subjects whose daily intake was <500 mg. In the Asian study Lau et al. also found that diet calcium intake < 498 mg/d increases the risk of hip fracture. The multivariate analysis in this study indicated the importance of paneer (cottage cheese), a major component of the north Indian diet, and it also highlighted the importance of calcium supplements. Although calcium intake was quantified on a daily basis, future studies could examine the protective effect per gram of calcium. Given that dietary calcium intake in most Asian countries is low; calcium supplements should have a considerable impact on the reduction of hip fracture risk. Like physical activity, this variable is of great importance with respect to public health measures that can decrease the likelihood of hip fractures and thus relieve much of the morbidity and mortality associated with this condition in the Indian population.
Much like calcium, adequate vitamin D is essential for bone strength. Although the importance of almonds in the multivariate model was not apparent, intake of fish significantly decreases the risk of hip fracture in the population studied. Since vitamin D3 (with calcium) has been shown to reduce the risk of hip fractures in other elderly populations and the fact that the Indian population is considered Vitamin D deficient[1, 8, 9], the effect of sunlight and other vitamin D containing foods should be examined for their effect on hip fracture incidence. Moreover, although some trials demonstrate that calcium and vitamin D supplementation is effective others fail to indicate an effect of vitamin D alone [22, 23]. Hypotheses regarding vitamin D deficiency in the urban Indian population include poor sunlight exposure, skin pigmentation, atmospheric pollution, and a vitamin D deficient diet[1, 8]. Awumey et al. also reported altered vitamin D metabolism in cultured skin fibroblasts from Indians.
The effect of caffeine was estimated mainly by the consumption of tea- an extremely popular beverage with the Indian population. It is evident that increased intake of tea significantly increases the risk of hip fracture, however in order to get a more accurate estimate of the risk of caffeine, a future more nuanced analysis may be required to account for the protective effect of the milk within the tea. It is also important to separate subjects based on the quantity of milk in their tea as some individuals may enjoy black tea and others may like to add milk. In India, the majority prefer to add milk, albeit in varying amounts to their tea. Although previous research indicates that the effect of habitual tea drinking on bone density is minor and does not significantly alter the risk of fractures in an American population, this particular variable may be significant in the Indian population as 90% of the cases and 81% of the controls were regular tea drinkers.
A major limitation of the study is the relatively limited sample size which impacted the power to detect the effect of certain variables deemed relevant by previous literature such as hormone/estrogen therapy, thyroid hormone, alcohol consumption and smoking (there were only 3 smokers, all men). Other potential risk/protective factors were not assessed such as exposure to sunlight or bone mineral density.
Hormone/estrogen therapy had a protective effect on women when considered alone, however the power of the study to evaluate this effect in detail was limited due to the small sample size. Nonetheless, it is consistent with the hypotheses of other research studies that both recent and prolonged use of this therapy has a protective effect on bone density and thus decreases the risk of fractures. Similarly, although 6 case members and 0 control members took thyroid hormone, the sample size was too small to estimate the effect of this drug on the risk of hip fracture. This is a potentially important variable as there is a current controversy about whether thyroid hormone may lead to osteoporosis and whether its use increases fracture risk at a clinical level.
This study indicated a potential inverse association with alcohol consumption and risk factor- again the sample size was inadequate to make a statistically significant determination. Previous research, like that of thyroid hormone, is controversial- some studies indicate that alcohol consumption weakly reduces risk of hip fracture, others suggest that there is no association between the two, and still others suggest that increased alcohol consumption increases the risk of hip fracture . It may be difficult to distinguish a potential protective/risk effect of alcohol on the bone versus the increased risk of falling due to increased alcohol consumption.
It is also important to mention that as with all case-control investigations, there is a possibility of recall bias and it is not possible to validate the information provided by the subject. However, given these constraints, valuable information was retrieved from the analysis.
Unlike many previous studies that focused on women, this investigation included both males and females. The distribution of hip fracture by age and sex was found to be different from that in the western counterparts studied in other investigations[1, 11, 12]. As mentioned earlier, 50% of Indian women and 36% of Indian men over the age of 50 suffer from osteoporosis and are at risk for hip fracture. Notwithstanding the high prevalence of osteoporosis and related hip fractures in India, and the resulting morbidity and mortality associated with the condition, there is no prior existing research on the risk factors of hip fractures in the Indian population. Given this formidable public health problem, the results of this study may be beneficial on a national level. If further research substantiates the importance of these variables, increasing activity level, calcium and vitamin D intake, decreasing caffeine intake, and maintaining a healthy BMI may decrease the prevalence of hip fractures in the country. In addition to emphasizing these dietary and lifestyle improvements, public awareness programs can encourage early screening and treatment strategies. These would help to further reduce the prevalence and thus morbidity and mortality of hip fractures in India.