Bioactive compounds in prunes may reduce osteoporosis risk

Worldwide, one in three women over the age of 50 years and one in five men will experience osteoporotic fractures in their lifetime, according to estimates from the International Osteoporosis Foundation. 

The body breaks down old bone cells and replaces them with new bone tissue. However, bone mass stops increasing around the age of 30 and after the age of 40, bone cells may begin to break down at a faster rate than new ones are formed, causing osteoporosis, according to the National Institute on Aging.  

This can be caused by multiple factors including inflammation and oxidative stress, which is when free radicals and antioxidants are unbalanced in the body, wrote researchers from the Pennsylvania State University who conducted the review of previously published studies.  

They found that prunes (Prunus domestica L.) can help prevent or delay bone loss in postmenopausal women. This is possibly due to their ability to reduce inflammation and oxidative stress, both of which contribute to bone loss, they said. 

Medical treatment for osteoporosis exists but there is growing public interest in finding nutrition-based strategies to treat the condition.  

The review, which was supported by the California Dried Plum Board, was recently published in the peer-reviewed journal Advances in Nutrition. 

Connie Rogers, associate professor of nutritional sciences and physiology and co-author of the review said: "In postmenopausal women, lower levels of oestrogen can trigger a rise of oxidative stress and inflammation, increasing the risk of weakening bones that may lead to fractures. Incorporating prunes into the diet may help protect bones by slowing or reversing this process." 

Mary Jane De Souza, professor of kinesiology and physiology, said: "Fruits and vegetables that are rich in bioactive compounds such as phenolic acid, flavonoids and carotenoids can potentially help protect against osteoporosis with prunes in particular gaining attention in previous research."  

Prunes contain minerals, vitamin K, phenolic compounds, and dietary fibre. 

Inhibiting inflammation and suppressing oxidative stress markers 

As part of the review, the researchers analysed data from 16 preclinical studies in rodent models, ten preclinical studies and two clinical trials. They found evidence that eating prunes helped reduce inflammation and oxidative stress and promoted bone health in all the studies. The clinical trials found that eating 100 grams of prunes -- about 10 prunes -- each day for one year improved bone mineral density of bones in the forearm and lower spine and decreased signs of bone turnover. Additionally, eating 50 or 100 grams of prunes a day for six months prevented loss of total bone mineral density and decreased TRAP-5b – a marker of bone resorption – compared to women who didn't eat prunes.

"Taken together, evidence from in vitro, preclinical studies, and limited clinical studies suggest prunes may help to reduce bone loss," Rogers said. "This may be due to altered bone turnover and by inhibiting inflammation and suppressing markers of oxidative stress." 

One potential mechanism for the positive effects could be that prunes trigger a change in the gut microbiome that then lowers inflammation in the colon. This may then, in turn, lower levels of pro-inflammatory cytokines and markers of oxidative damage, suggested the researchers.  

Previous research: calcium and soy reduce osteoporosis fracture risk 

Dietary intakes of calcium, magnesium, and soy isoflavones have been found to influence the risk of osteoporotic fracture incidences. A 61,000-strong study found that dietary calcium consumption was inversely related to a lower risk of osteoporotic fractures but high magnesium consumption was related to an increased risk. The same study also found that high intakes of total soy isoflavone and isoflavone components (genistein, daidzein, or glycitein) were linked to a lower risk of osteoporotic fractures in men.