Women who ate a Mediterranean diet had a slightly lower risk for hip fracture, compared with women who ate other healthy diets, a post hoc analysis of the Women's Health Initiative (WHI) found.
After adjustments, women scoring in the highest quintile for Mediterranean diet adherence reported a lower risk for hip fracture (hazard ratio (HR) 0.80, 95 CI 0.66-0.97), and had an absolute risk reduction of 0.29%, compared with women who ate the DASH diet or adhered to the 2010 U.S. Dietary Guidelines, Bernhard Haring, MD, MPH, of the University of Würzburg in Germany, and colleagues, reported in JAMA Internal Medicine.
Haring's group looked at total bone fractures and hip fractures reported among 90,014 women, ages 50-79, who were enrolled in the WHI from 1993 to 1998 and followed for a median of 16 years through 2014.
Excluding, toe, finger, clavicle, and sternum fractures, which were deemed unlikely to be related to bone mineral density, 2,121 cases of hip fractures, and 28,718 total fracture cases were self-reported.
The WHI participants' food frequency questionnaires (FFQ) were assessed for dietary intake and categorized by adherence to one of four diets: the 2010 U.S. Dietary Guidelines (HEI-2010), the Alternative Healthy Eating Index (AHEI-2010), the DASH diet, and the alternate Mediterranean Diet (aMED).
After adjustments, women who scored in the highest quintile of aMED index scores reported a lower risk for hip fracture with number needed to treat of 342. However, no association was found between the aMED diet and the total fractures (HR 1.01, 95% CI 0.95-1.07).
Better HEI-2010 or DASH scores were also associated with lower hip fracture risk, but the results did not reach significance (Q5 HR 0.87, 95% CI 0.75-1.02, and Q5 HR 0.89, 95% CI 0.75-1.06, respectively). No associations were found between the AHEI-2010 scores and fracture risk.
A secondary analysis taking fall history into account did not change the main results.
But other nutrition researchers questioned the study's significance.
"Had physical activity been measured even somewhat better, it is likely that the observed inverse association between diet quality and risk of hip fracture would have become nonsignificant," Walter C. Willett, MD, DrPH, of the Harvard T. H. Chan School of Public Health, wrote in JAMA Internal Medicine. "Although pattern analysis can be useful and stronger associations are often seen when multiple aspects of diet contribute to the risk of the outcome or the effects of multiple components are synergistic, pattern analysis can also dilute and obscure a causal association with diet if only one or a few components of diet are causally related to the outcome."
Willett noted, though, that many long-term, controlled-feeding studies have supported the role of Mediterranean-type diets for prevention of multiple other health conditions.
And Bess Dawson-Hughes, MD, of Tufts University in Boston, said she agreed with Willett. "Physical activity is a potential confounder in this study."
"I think there are already well-established reasons to recommend the Mediterranean diet for conditions other in bone. This is an effective diet in reducing cardiovascular disease, and somewhat supportive for lowering fracture risk," Dawson-Hughes said in a phone interview with MedPage Today. "These findings do not change my enthusiasm for the Mediterranean diet. I don't think it's even necessary to even try to promote it for osteoporosis."
One nutrition researcher contacted by MedPage Today said the research had some credibility.
Martin Kohlmeier, MD, PhD, of UNC School of Medicine and Public Health, told MedPage Today in an email that he suspected that a higher than average tomato/lycopene consumption with the Mediterranean pattern might be involved with the prevention mechanism.
"It has been shown to be associated with reduced risk of hip fracture in the Framingham cohort (Sahni et al, 2009), and there is supporting evidence from other studies in humans and in animals," Kohlmeier wrote.
But Marion Nestle, PhD, MPH, of New York University, told MedPage Today she believed nondietary confounders were relevant. "[P]eople who consume healthy diets also tend to have other healthy lifestyle behaviors; they don't smoke cigarettes or drink much alcohol (known risk factors for fractures) and they are physically active (protective against fractures)."
Fang Fang Zhang, MD, PhD, of Tufts University in Boston, agreed that the roles of physical activity or vitamin D couldn't be ruled out in reducing fracture risk. "Overall, I would interpret with caution given residual confounding cannot be ruled out," Zhang said. "The potential mechanism cannot be identified from the current study but there are some suggestions that specific dietary components play a role."
"Nevertheless, I hope that we are getting into the era of establishing the science of nutrition by evidence based data," Iris Shai, RD, PHD, of Ben-Gurion University in Israel, said in an email to MedPage Today. "This study might be a good step to further follow-up studies for younger women, for metabolic studies to specify mechanism of action and for randomized controlled clinical trials that could lower the risk of residual confounding and improve a causal association."
Study limitations included population limited to postmenopausal women in overall good health, the use of a food intake questionnaire could not fully assess dietary nutrient intake, and potential misclassification of self-report fractures.
None of the authors reported any relevant financial relationships with industry.
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