Polyphenol Powerhouses: Beyond Calcium for Bone Health
Calcium and vitamin D: you know them, you love them, and they are essential for bone health as we age. But to get the most out of your diet when it comes to preventing or managing osteoporosis, you may want to consider incorporating these unexpected foods.
Key Takeaways:
The most important nutrients for bone density are calcium, vitamin D, and protein. If you don’t already have that dialed in, start there!
Higher intake of fruit and vegetables is associated with greater retention of bone density into old age and reduced risk of fractures. These foods tend to be low in calcium but are high in other micronutrients like vitamin C and magnesium that are important for bone health.
Polyphenols may play a role in preserving bone mass, but not all polyphenol-rich foods are created equal, and supplements provide lackluster results.
Prunes have the strongest evidence to support their role in preserving bone mass and reducing the risk of fractures in post-menopausal women. High intake of tea and extra virgin olive oil are also associated with reduced risk of osteoporosis, fractures, and bone density loss.
Polyphenol-rich foods should supplement, not replace, a comprehensive plan that includes nutrition, lifestyle, and medication (if needed).
But First, A Quick Review on Bone Health:
Bone density peaks between 25 and 30 in women and slowly declines until after menopause, when the steep drop in estrogen accelerates bone density loss. Other factors like decreased vitamin D synthesis, reduced calcium absorption, and increased loss of calcium from bone also contribute to age-related bone loss in both women and men. Although some bone mineral density (BMD) loss is normal and expected with age, significant loss of bone density can lead to osteoporosis (or osteopenia, which is less severe BMD loss). These conditions are exceedingly common; roughly 50% of women over 50 have osteopenia and 20% have osteoporosis [1].
Medications, lifestyle, and nutrition all play a role in preserving bone mass to help prevent and manage bone loss. Calcium, vitamin D, and protein are undoubtedly the most important micronutrients when it comes to bone health; everything else covered in this article comes second. Here’s the quick and dirty:
Adult women under 51 need 1000mg of calcium, and those over 51 need 1200mg daily.
Excellent sources of calcium include dairy products (except butter, sorry!), fortified non-dairy beverages, sardines with the bones, and tofu set with calcium sulfate.
Plant sources like greens (especially spinach, collard greens, and kale), white beans, and soybeans are also good sources but contain significantly less calcium. They also have other compounds that reduce the amount of calcium that is absorbed.
Getting calcium from food is best, but if you need some help, supplement, supplement, supplement! Keep each supplement dose under 500mg.
Adult women under 70 need 600 IU (15 µg) of vitamin D, and those 71 and older need 800 IU (20 µg) daily
Food is not a major source of vitamin D; most of our vitamin D is made by the body when we are exposed to sunlight.
It is common for older adults to require a vitamin D3 supplement, as vitamin D needs are higher and our ability to make it decreases with age.
Supplementing with 800 - 1000 IU of vitamin D3 has been shown to reduce fracture risk in post-menopausal women [2].
Most calcium supplements contain vitamin D, so be careful not to over-supplement, because vitamin D builds up in the body.
Adult women should aim for 1.2 - 1.6 grams of protein per kg of body weight (or .54 - .73g per lb), especially post-menopausal women
It has long been disproven that high protein intake contributes to bone loss, yet the myth persists.
If you get enough calcium and vitamin D, protein intake actually protects bones. It also helps preserve muscle mass needed for balance, strength, and fall prevention.
Stick to lean protein sources like chicken, turkey, fish; and plant-based sources of protein such as high-protein tofu, tempeh, and seitan.
Beyond Calcium for Bone Health
Overall Diet Quality
Multiple large-scale studies including the Women’s Health Initiative and meta-analyses have found that overall diet quality is associated with higher bone density and reduced risk of fractures.
The Mediterranean Diet (ever heard of it?) is one of the best-studied eating patterns for osteoporosis. Following a Mediterranean Diet pattern has been associated with significantly greater bone mineral density and reduction in osteoporosis prevalence and hip fractures [3, 4, 5, 6]. Eating enough protein, meeting micronutrient needs through a diverse diet, and avoiding excess alcohol consumption (more than 3 drinks per day) are all hallmarks of a healthy eating pattern that protects bone health. High fruit and vegetable consumption (at least 5 servings a day) is another feature of the Mediterranean Diet that is associated with better bone density and reduced fracture risk [3, 7, 6, 8]. Although most fruits and vegetables tend to be low in calcium, they are rich in other micronutrients including magnesium, vitamin C, phosphorus, and vitamin K that play a critical role in bone health.
Polyphenols
Fruits and vegetables may have another unique advantage: polyphenols. Polyphenols are beneficial compounds found only in plants. Resveratrol, EGCG, and curcumin which is found in turmeric are some better-known examples of the 500+ polyphenols commonly found in food. Polyphenols are thought to protect bones through their anti-oxidant and anti-inflammatory effects, and may even increase the number and activity of cells that build bone (osteoblasts) and inhibit those that break down bone (osteoclasts) [9].
Multiple studies have connected polyphenol intake with improved bone health. One meta-analysis of 13 randomized controlled trials found that intake of foods high in anthocyanin, a polyphenol found in red and purple-colored foods like berries and red cabbage, were significantly associated with increased spine bone mineral density (but not other sites, such as hip) in older adults at risk of osteoporosis [10]. Another study that included over 10,000 adults found that those with the highest take of a group of polyphenols called flavonoids had greater total and site-specific femur bone density and a lower risk of osteoporosis [11]. This is supported by another study done on 3,000 perimenopausal women, which found that higher flavonoid intake (mostly from tea – more on that later) was associated with greater bone density at the hip and spine [12]. These exciting findings will hopefully pave the way for more research that explores the role of dietary polyphenols in osteoporosis prevention and treatment.
When it comes to polyphenols, avoid the supplement aisle at all costs! They are most effective when consumed the old-fashioned way: in whole-food form. When polyphenols are extracted and consumed as the isolated compound, their beneficial effects don’t hold. This is because whole foods have a unique “food matrix”, the physical and chemical makeup of the food that interacts to dictate how that nutrients are digested, absorbed, and even act within the body. When polyphenols are consumed in food form, other structures and nutrients work together to enhance their effects.
Prunes
The humble prune is a rich source of polyphenols and has the largest body of research to support its role in preserving BMD. The Prune Study was a 12-month randomized controlled trial (RCT) that compared the effect of 50 grams (4-6) and 100g (10 - 12) of prunes daily on bone density at multiple sites, osteoporotic and hip fracture risk, and bone turnover markers and hormones in post-menopausal women [13].
The 4 - 6 prune group retained total hip BMD compared to the control group (no prunes) which lost BMD at the total hip. There was no difference between the 50g prune and 0g prune groups for other sites where BMD was measured, fracture risk, or bone markers [13].
The group that consumed 100g of prunes had a lower osteoporotic fracture risk compared to the control group. However, there was no difference for BMD, hip fracture risk, or bone markers. If the thought of eating 10 - 12 prunes a day makes your stomach hurt, you’re not alone. The 100g group had a much higher drop out rate than anticipated. This could have influenced the findings and may explain why there was a benefit to total hip BMD in the group that ate 50g of prunes but not 100g [13].
The combined 50g + 100g prune group preserved total hip BMD, which decreased in the control group. In addition, the risk of both a major osteoporotic fracture and hip fracture increased in the control group but was maintained in the prune group. No benefits were observed for BMD at other sites aside from the hip, or bone markers [13].
Another 6-month randomized controlled trial also compared the effects of eating 50g and 100g of prunes a day on BMD and bone biomarkers. There was no difference in site-specific BMD changes between the prune and control groups. Both the 50g and 100g group maintained total body BMD, which decreased in the control group. While maintaining total body BMD is certainly positive, it is more meaningful to see a benefit in site-specific BMD in areas of high fracture concern (the hip and spine). Over the course of the study, both prune groups had reduced levels of an enzyme that participates in the breakdown of bone (bone resorption) called TRAP-5b [14].
A third RCT compared the effects of consuming 100g of prunes to 75g of dried apples for 12 months on bone mineral density and bone markers. Compared to the apple group, the prune group retained more bone mass at the forearm and spine than the control, but not in the hip or total body. Osteocalcin, a marker of bone turnover (both formation and resorption), was higher in the apple group than the prune group at the end of the study. Apples also contain polyphenols that could have provided benefits, so it wasn’t a true control group. This study also had a very high dropout rate, which could have influenced the results [15].
These three RCTs demonstrate that eating at least 4 - 6 prunes daily may help preserve bone mass in post-menopausal women. To reduce fracture risk, 4 - 6 prunes (50g) may not be enough. The one study that looked at fracture risk only saw an impact in the group that ate 100g of prunes daily, and in the combined 50g + 100g group. This suggests it may take more than 4 - 6 prunes to reduce fracture risk, although how much more is unclear. Although the studies consistently showed that prune consumption helped maintain BMD in at least one area, they disagreed on where. This could be due to many factors such as different calcium and vitamin D supplementation dosages, study length, inter-machine variability, high dropout rates, and participant characteristics.
Putting it into action: Prunes are safe to consume and may even benefit heart and gut health. If you want to give them a try, start slowly with one prune after each meal for a week and increase one at a time until you reach 4 - 6 prunes daily to avoid the same fate as the 100g prune groups.
Other Polyphenol-Rich Foods
Tea and olive oil are also packed with polyphenols and may have bone-protective effects. Most of these foods have only been associated with better bone health, unlike prunes which have multiple randomized controlled trials to back up their efficacy.
Green and Black Tea
The association between regular tea consumption and bone health has been documented for over 30 years, beginning with the MEDOS (Mediterranean Osteoporosis) Study conducted across 6 European countries, which reported that tea consumption was associated with a reduced risk of hip fractures [16].
One 10-year long Australian study on women over 70 found that for each additional cup of black tea consumed daily, there was a 10% reduction in any osteoporotic fracture during the study period [17].
Findings from the massive UK Biobank study showed that consumption of 3-4 cups of tea per day was associated with 15% reduced risk of osteoporosis in adults. And good news for coffee lovers: those who consumed 1-2 cups of both coffee and tea had the lowest risk of osteoporosis [18].
A study on over 40,000 Taiwanese adults (45 - 74 years old) found that the risk of osteoporosis was lower in those who had low (1 - 4 times a week) and high tea (5 - 7+ times a week) consumption compared to no tea consumption [19].
While these types of studies don’t prove that tea protects bone density, drinking a few cups of green and/or black tea daily (skip the sweetener and milk, if you can) is generally safe and has consistently been associated with improved bone health.
Extra Virgin Olive Oil
The many benefits of olive oil may also extend to bone health. In addition to being a main component of the bone-benefitting Mediterranean Diet, its high polyphenol content may also protect bones.
An observational study conducted using data from the PREDIMED trial which assigned older adults to various Mediterranean diet patterns to assess cardiovascular risk found that those who consumed the most extra virgin olive oil (4 tablespoons on average) had a 51% lower fracture risk over the course of the study compared to those who consumed the least (2.7 tablespoons on average). However, this association only held for extra virgin olive oil – which is the least refined and highest in polyphenols – not for regular olive oil or other cooking oils [20].
Another study on Spanish women found no difference in areal BMD based on olive oil consumption, but did report a difference in volumetric BMD. Areal BMD is determined from a 2-D image of bone size measured by DEXA scan, and what is commonly referred to as “BMD.” Volumetric BMD is determined from a 3-D image of the bone that can give a better picture of the actual mineral concentration in different parts of the bone. Those who consumed over 4 teaspoons (1.3 tablespoons) of olive oil daily had greater volumetric BMD overall, and in the interior (trabecular) and hard exterior (cortical) areas of the bone [21].
Preliminary findings from a study conducted in Italy on adults over 50 found that extra virgin olive oil (as well as fruit and fish) consumption was specifically associated with higher T-scores, a measure of an individual’s bone density relative to the average BMD of young adults [22].
Although these findings are exciting, like tea, the jury is still out on whether there is a causal connection between olive oil consumption and bone health. Chances are you may already cook with olive oil, so to get the most out of it, make sure you’re using extra virgin olive oil, and incorporate it wherever you can as your go-to oil: for cooking, as salad dressing, and finishing vegetables, soup, or pasta dishes.
In Summary
Although there are very few randomized controlled trials in this area, observational studies consistently associate polyphenol-rich dietary patterns and specific foods with increased preservation of bone density, and reduced risk of osteoporosis and fractures. Prunes are one of the few foods with multiple RCTs to back up their efficacy in preserving BMD, and possibly even reducing fracture risk. Aim for at least 4 - 6 prunes daily to get the bone benefits.
Tea and extra virgin olive oil are two other foods that pack a serious punch of polyphenols and have been associated with improved BMD, reduced osteoporosis risk, and reduced fracture risk. More research is needed to confirm the impact of these foods on bone health, and the amount you should consume to get the benefits. But, in the meantime, you can sip on tea and drizzle olive oil knowing that you just might be doing your bones a favor, in addition to reaping all the other established health benefits.
Incorporating more polyphenol-rich foods is a worthy endeavor that aligns with an overall healthy eating pattern, and will positively impact health far beyond your bones. But, it should supplement a well-rounded approach that includes proper nutrition, physical activity, and medications if you and your doctor decide they are right for you.
