Are fruits and vegetables beneficial for bone health in postmenopausal women?
Fruits and vegetables contain calcium, potassium, magnesium, B vitamins, vitamins C, E and K, various antioxidants and phytochemicals, all of which can be beneficial for bone health. Some studies have reported that diets high in fruits and vegetables are linked to better bone health in postmenopausal women1,2; however, these positive findings are not consistent across the current scientific literature. Because studies can be of different scientific quality, our group performed a systematic review of the existing literature, assessed the quality of the different studies, summarized the findings, and identified potential research gaps3.We reviewed studies that have examined the associations between fruit and vegetable intake and the incidence of osteoporotic fractures, bone mineral density and bone turnover markers in women >45 years.
Assessing studies for risk of bias
We searched electronic databases and reference lists of selected articles for peer reviewed manuscripts that were published in English scientific literature. We included observational studies and clinical trials that specifically reported fruits and vegetables intake as a main dietary exposure among community dwelling women. Two reviewers independently selected and extracted data from the studies and evaluated the risk of bias. To assess the risk of bias in observational studies, we developed a tool that consists of seven domains3. The risk of bias in clinical trials was assessed using the Cochrane Collaboration’s tool4 slightly modified to reflect dietary studies. This tool also consists of seven domains. The assignment of low, moderate or high risk depended on the number of domains considered not to be biased. Studies are considered of high quality when there is low risk of bias and of low quality when there is a high risk of bias.
After a detailed review of all the studies, we included eight studies. One cohort study reported cross-sectional as well as longitudinal data in the same study population. There was significant heterogeneity in design, definition and amount of fruit and vegetable intake, outcomes, analyses and reporting of results among the different studies. Two studies had low, two had moderate and four had high risk of bias. Overall, randomized controlled trials and prospective cohort studies found no beneficial effects of fruits and vegetable intake, while one case-control and all the cross-sectional studies found favorable relationships between fruit and vegetables intake and indicators of bone health.
In general, randomized controlled trials and prospective cohort studies have less potential for biases, and are often viewed as better study designs to answer the question of whether a certain intervention has its desired effects. In cross-sectional studies, fruit and vegetable intake may be linked to better bone health not because of the effect of fruit and vegetables, but because of the other healthy behaviours and lifestyles that are associated with a high fruit and vegetable intake such as physical activity, not smoking or taking calcium and vitamin D supplements.
Recommendations for future research in this area
The studies assessed in our review had different methods of assessing intake, different definitions or classification of fruits and vegetables, different intake levels, different types and usage among the various study populations. For example, some studies included potatoes, pulses and starchy vegetables in the vegetable group, or fruit juices and nuts in the fruit group. This may dilute a positive effect of fruits and vegetables on bone health and reduce the ability to detect an association.
There is a need for researchers to assess dietary intake using comparable and standardized methods across populations. A World Health Organization report provides useful guidelines for the assessment of fruit and vegetable intake5. Complying with these guidelines will result in more comparable literature, facilitate future systematic reviews and meta-analyses and ultimately lead to the development of evidence-based dietary recommendations.
In conclusion, our systematic review of the scientific literature did not find a clear beneficial effect of fruits and vegetables on bone health for women aged >45 years. However, our review was limited by the small number of well-conducted studies in this area, and the differences in the assessment of fruit and vegetable intake.
- Xu L, Dibley M, D’Este C, Phillips M, Porteous J, Attia J 2009 Food groups and risk of forearm fractures in postmenopausal women in Chengdu, China. Climacteric 12(3):222-229.
- Tucker KL, Hannan MT, Chen H, Cupples LA, Wilson PW, Kiel DP 1999 Potassium, magnesium, and fruit and vegetable intakes are associated with greater bone mineral density in elderly men and women. Am J Clin Nutr 69(4):727-736.
- Hamidi M, Boucher BA, Cheung AM, Beyene J, Shah PS 2011 Fruit and vegetable intake and bone health in women aged 45 years and over: a systematic review. Osteoporos Int 22(6):1681-1693.
- The Cochrane Collaboration. (2009). “Cochrane Handbook for Systematic Reviews of Interventions- Version 5.0.2.” from http://www.cochrane-handbook.org/.
- Agudo, A. (2005). “Measuring intake of fruit and vegetables.” from http://www.who.int/dietphysicalactivity/publications/f&v_intake_measurement.pdf