Nutrition & Lifestyle: Beyond Calcium and Vitamin D — Plant Antioxidants Strengthen Bone Health
During the past few decades, osteoporosis has emerged as a major public health concern among the booming older adult population. Approximately 10 million Americans have osteoporosis, while another 44 million have low bone density, placing them at increased risk of the condition.1 Women especially are vulnerable to increased bone loss during and after menopause.
Medications to treat osteoporosis have been effective, but there are no FDA-approved drugs that can help prevent it. Calcium plus vitamin D supplementation along with exercise have been the mainstays of prevention, but studies on these measures have shown only marginal improvement in slowing bone loss.2,3 Although dietary calcium does lower bone turnover by about 10%, it hasn’t been demonstrated to reduce bone fracture rates.
Evidence from research studies continues to suggest that certain vitamins, minerals, food groups, and even dietary patterns play an important role in skeletal health. For example, greater fruit and vegetable intakes have been associated with higher bone mineral density (BMD), along with less BMD loss over time.4 Recently, the role of plant-derived compounds has been examined, based on the idea that certain phytochemicals increase the rate of bone deposition by osteoblasts (cells that secrete the matrix for bone formation) and decrease the rate of bone breakdown by osteoclasts (cells that break down bone). Some studies have implicated oxidative stress in the pathogenesis of osteoporosis.
Bone health depends on a dynamic equilibrium maintained between the constant production of new bone via osteoblasts and the resorption of old bone by osteoclast activity. Osteoblasts synthesize collagen and protein for the bone matrix and promote calcification. In osteoporosis, bone mass and density decrease with the loss of bone matrix and mineralization; bone resorption exceeds bone formation, leading to thin, fragile bones subject to spontaneous fracture.
The Framingham Osteoporosis Study (an ancillary study of the Framingham Heart Study) also investigated vitamin C in suppressing osteoclast activity through its antioxidant action. The study reviewed data from food-frequency questionnaires along with BMD among the original cohort of subjects between the ages of 68 and 96.4 Men with higher dietary vitamin C intake showed less femoral neck BMD loss compared with the lowest tertile of dietary vitamin C consumption. For both genders, participants in the highest category of supplemental vitamin C intake had 69% fewer hip fractures compared with nonsupplement users.
Bone resorption (when osteoclasts break down bone tissue and release minerals, resulting in a transfer of calcium from bone to the blood) appears to be affected by certain plant compounds. Common fruits, such as oranges and prunes; vegetables including tomatoes, green beans, cucumbers, broccoli, and lettuce; the herbs dill, sage, garlic, parsley, thyme, and rosemary previously have been classified to possess bone resorption–inhibiting properties (BRIPs).9 In a 2015 study, healthy postmenopausal women were randomized to receive either a diet of at least nine daily servings of vegetables, herbs, and fruit classified as containing BRIPs; nine daily servings of ad lib vegetables; or their usual diet. The group consuming plant foods with the highest content of BRIPs showed a significant decrease in bone turnover markers compared with the other dietary groups.10
Thus, geriatricians should remember to practice food first. Diets rich in fruits and vegetables contain both a plethora and expansive variety of phytochemicals that have been shown to suppress the proinflammatory milieu and bone loss associated with aging. Data from the Framingham research suggest that subjects who consumed the most fruits, vegetables, and cereal grains had the greatest BMD at all bone sites.
It’s important to reinforce the USDA’s dietary guidelines aimed at five to 13 servings of fruits and vegetables daily.3 Demonstrating to older adults what constitutes a portion size of these plant foods would be useful, especially since the Centers for Disease Control and Prevention reports that only 1 in 10 adults consumes enough.15
Adequate calcium and vitamin D intake remain a nutrition focus for bone health. The Recommended Dietary Allowance (RDA) for calcium is 1,000 mg for men and 1,200 mg for women aged 51 to 70; beyond the age of 70, the RDA is 1,200 for both. For best absorption, calcium should be consumed from food in amounts of 300 to 500 mg, as the body can’t absorb more than that at one time. Vitamin D facilitates calcium absorption and thus bone mass and strength. In addition, vitamin D affects muscle performance, balance, and risk of falling. However, it can be difficult, if not impossible, to get an adequate amount of vitamin D from food. The RDA for older adults (both men and women) aged 51 to 70 is 600 IU, and it increases to 800 IU beyond age 70. According to Beth Dawson-Hughes, MD, a professor of medicine and director of the Bone Metabolism Laboratory at Tufts University, vitamin D is limited to “foods that people don’t tend to eat daily like fatty fish.”3 She emphasizes that “a serving of most fortified cereals provides only 40 IU, and a cup of milk has just 100 IU.” Mushrooms, especially if exposed to sunlight, along with other fortified foods, such as dairy, are good sources of vitamin D, but for some people, a dietary supplement may be needed.
Dawson-Hughes also recommends protein, as it comprises about one-half of bone. She says, “Consuming protein stimulates insulinlike growth factor-1, a growth factor that builds both bone and muscle.” The RDA for protein for adults older than 50 is 46 g for women and 56 g for men, but this is a minimum. Some older adults may need more protein (1 to 1.2 g protein per kilogram of body weight). With increased rates of overweight and obesity, many older adults also are dieting. Care should be taken to avoid very low-calorie diets, as low BMD has been reported in obese women who consume fewer than 1,000 kcal per day.16
When working with older adults, practitioners need to emphasize a plant-based diet with nutrient-dense foods high in bioavailable vitamins, minerals, phytochemicals, and antioxidants that help to support bone health. Practitioners can seek opportunities to integrate these recommendations as part of a multidisciplinary team, serving seniors in both primary care and geriatrics settings.
— KC Wright, MS, RDN, is a research dietitian at Dartmouth Hitchcock Medical Center in New Hampshire and focuses on sustainable nutrition at wildberrycommunications.com.
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