May/June 2021

Nutritional Intricacies for Osteoporosis
By KC Wright, MS, RDN
Today’s Geriatric Medicine
Vol. 14 No. 3 P. 22

Dietary intervention is imperative.

Although 50 million Americans are at an increased risk for bone fractures, osteoporosis is both a preventable and treatable disease.1 One-half of Americans older than 50 already have osteoporosis or osteopenia.2 These progressive decreases in bone mass and deterioration of bone structure increase risk of fragility fractures, which are often associated with paralyzing pain that can cascade into physical disability, loss of independence, depression, and/or premature death.3 Some lifestyle factors, including exercise and nutrition, are known to play an important role in bone health and can help to reduce the risk of developing osteoporosis.

Americans fall woefully short in meeting the recommended intakes for many nutrients.4 In particular, calcium and vitamin D, critical for healthy bone, are considered dietary components of public health concern for the US population.5 According to the 2020–2025 Dietary Guidelines for Americans, most adults don’t consume adequate amounts of both calcium and vitamin D. Almost 30% of men and 60% of women lack sufficient calcium intake, while more than 90% of all adults don’t consume enough vitamin D. This is because most Americans don’t follow dietary patterns that include the recommended intake of dairy foods, foods fortified with vitamin D and/or calcium, and seafood.

Calcium & Vitamin D Conundrum
Almost all—99%—of the body’s calcium is stored in bone, with just 1% distributed among the blood, muscle, and other tissues. Calcium is embedded in collagen fibrils and is essential to bone rigidity. Vitamin D is critical for calcium absorption into bone, and, to a significant extent, regulates calcium homeostasis. Bone undergoes continuous remodeling with constant deposition and resorption of calcium into new bone. In aging adults, particularly postmenopausal women, resorption exceeds formation, resulting in bone loss that increases the risk of osteoporosis over time.

Standard practice to reduce osteoporosis and fracture risk has been to recommend supplements for those with inadequate dietary calcium or vitamin D intake, as they’re generally safe and inexpensive.6 The National Academies of Sciences, Engineering, and Medicine recommends daily intake of 1,000 mg of calcium for men ages 50 to 70, while women 51 and older and men older than 71 are told to consume 1,200 mg. There’s no evidence that intake above these levels provide additional benefits. For vitamin D, the National Academies recommends that both women and men consume 600 IU daily until age 70, and then 800 IU for those 71 and older.

There’s been some concern that taking calcium supplements in doses higher than recommended may cause hypercalcemia and lead to atherosclerosis. Although the relationship isn’t yet understood, both the National Osteoporosis Foundation and American Society for Preventive Cardiology have adopted the position that neither calcium from food nor supplements has any association with cardiovascular disease.7 It’s suggested that people don’t exceed the Tolerable Upper Intake Level for calcium of 2,500 mg per day from food and supplements.

Food Sources and Bioavailability: Calcium and Vitamin D
The bioavailability of calcium varies among different foods sources. Although dairy foods are a significant source of calcium, only about 30% of the mineral may be bioavailable.8 For example, the Nutrition Facts label on a carton of low-fat milk may list calcium content at 300 mg per cup, yet only about 100 mg will be absorbed and used by the body. Plant foods, such as kale and spinach, contain less calcium overall, but have a higher bioavailability (around 50%). A cup of cooked kale contains approximately 180 mg calcium, of which 90 mg are bioavailable. Thus, a cup of milk and a cup of cooked kale contain about the same amounts of bioavailable calcium.

However, some plant foods also contain naturally occurring compounds designed to protect the plant from bacteria and insects.8 These compounds are referred to as “antinutrients” because they can block absorption of nutrients. Oxalates and phytates are examples of antinutrients that bind to calcium and reduce its bioavailability. Among edible leafy greens, spinach contains the most calcium, 260 mg per cup cooked. Yet spinach is also high in oxalates that reduce calcium bioavailability to just 5%, or about 13 mg per cup. This dialogue may be confusing for patients, yet the bottom line is that spinach and most plant foods contain many other valuable nutrients, even though they’re not necessarily significant bioavailable sources of calcium. Patients can be advised to consume spinach when other calcium-rich foods are not being served, or at a different time than when taking calcium supplements. Fortunately, Recommended Dietary Allowance (RDA) levels are established to consider calcium bioavailability of foods.

When considering calcium absorption, the percent absorbed depends upon the amount of elemental calcium consumed from both food and dietary supplements at a given time. As calcium intake increases, the percentage of absorption decreases.9 Maximal calcium absorption will occur when intake is <500 mg at one time.10 Therefore, consumption of calcium through both food and supplements should be spread throughout the day. Further affecting bioavailability of calcium is the fact that it competes with other minerals, especially magnesium, for absorption. When anticipating benefits from improved calcium intake from both food and supplements, it’s imperative to ascertain all of the other dietary supplements a patient may be taking.

Vitamin D is obtained from cutaneous synthesis after exposure to sunlight, with varying amounts among population and geographic locations. From food, vitamin D occurs naturally in limited dietary selections, such as fatty fish, mushrooms, and egg yolks. Some foods, such as dairy products and certain cereals, are fortified with vitamin D. As the only significant plant food source of vitamin D, mushrooms also have the ability to synthesize vitamin D when exposed to ultraviolet (UV) light. Thus, wild mushrooms are an excellent source of vitamin D, while commercial growers have begun to add UV light treatment during the production process for a comparable nutrient value to that of indigenous plants. However, mushrooms produce vitamin D2, whereas humans produce vitamin D3, which is thought to be significantly more effective in increasing serum levels of the nutrient.11

Postmenopausal Women
One of every three postmenopausal women is affected by osteoporosis and thus has a higher risk for developing fragility fractures than for breast cancer, which has bypassed lung as the most common form of cancer.3 Women of this age are at the greatest risk for developing osteoporosis as the production of estrogen ceases, causing a decrease in calcium absorption and an increase in bone resorption. With almost 50 million postmenopausal women in the United States, osteoporosis and its related bone fracture are a major public health concern.

Studies on bone density and calcium intake in postmenopausal women have had mixed outcomes. One possible reason for this is that the research considered only supplemental calcium without consideration of the contributions of dietary calcium.12 Other research failed to account for any women taking hormone replacement therapy or other supplements that may reduce bone loss, such as vitamin D.8 Results of systematic review and meta-analysis found that higher calcium intake, typically with a supplement, was associated with improved bone mineral density (BMD) and slightly lower hip fracture risk,6 which justifies the higher RDA for calcium for postmenopausal women compared with younger females.

In older adults who are institutionalized, supplementation with calcium and vitamin D has been shown to be effective in reducing fractures and falls. Yet in community-dwelling adults older than age 50, the effect of these nutrients on fractures is less clear. In 2018, the US Preventative Services Task Force (USPSTF) concluded that there’s insufficient evidence to assess the balance of benefits and risks of calcium and vitamin D alone or combined for the primary prevention of fractures in most community-dwelling adults without fracture risk or osteoporosis.13 Rather, the USPSTF directly recommends against the use of calcium and vitamin D supplements to prevent fractures in community-dwelling postmenopausal women not at risk for falls, fractures, osteoporosis, or vitamin D deficiency.

Dried Plums to the Rescue?
In 2001, US plum growers were authorized by the FDA to call prunes “dried plums” in an effort to increase appeal among consumers. Dried plums (Prunus domestica L.) remain commonly referred to as prunes, but beyond their traditional use in helping to facilitate laxation, their role in bone health has been considered in both preclinical and clinical research.

The dietary fiber in dried plums has made the fruit well known for its effect on gastrointestinal motility. A serving of four prunes contains about 2.4 g of fiber. The laxative effect may also be influenced by the significant amounts of phenolics present as well as sorbitol in the fruit.14

Dried plums are a good source of potassium and vitamin K, two additional nutrients that also have a supportive role in bone health.15,16 In fact, dried plums are higher in vitamin K (22.8 mcg per serving) compared with other fruits commonly consumed, which may influence bone health by helping to enhance calcium balance.

Dried plums contain significantly more of the trace mineral boron than do other fruits and vegetables.17 A serving of dried plum contains about 1.1 mg of boron, two to three times as much as a serving of pears, apples, and grapes. Boron has been shown to stimulate bone growth and bone metabolism and play an important role in preserving BMD.18

Recent research on dried plums has focused on their so-called distinct nutrient and bioactive dietary character beneficial to bone health. Specifically, dried plums are high in phenolic compounds of which neochologenic and chlorogenic acids are the most predominant.19 Polyphenols also function as antioxidants that may protect against bone loss linked to oxygen-derived free radicals in the bone microenvironment.

In a comprehensive review to identify potential effects that dried plums may have on bone health, it was suggested that the fruit enhances bone formation and inhibits bone resorption.14 Although the mechanism of action isn’t clear, the polyphenols may act on cell signaling pathways that influence osteoclast and osteoblast differentiation. Results on specific markers of bone turnover weren’t consistent across and between studies. The intervention phase of studies reviewed was between three and 12 months, which may have been a limited opportunity to note significant changes in BMD.

In a small clinical study of postmenopausal women with osteopenia, daily consumption of 50 g of dried plum (five to six dried plums) for six months was associated with a reduction in loss of total body BMD.18,20 It’s important to note that all of the research on prunes and bone health discussed here has been associated with funding from the California Dried Plum Board. Large-scale clinical trials, especially on postmenopausal women, are needed to determine any bone protective effect of dried plums with fractures and BMD as primary endpoints.

The benefits of dried plums may be due to their combined bioavailability of nutrients and phenolics. Similar to other nutrient-dense foods, the whole fruit is more efficacious than are isolated components due to the synergistic effects within the complete edible matrix. The Dietary Guidelines for Americans recommend consuming whole fruit, not fruit juice, extract with fruit, or fruit flavorings. Studies using whole foods are more difficult to control because of their variable and complex composition.21 Certainly, dried plums are a nutrient-dense food, and if consumed by older adults to aid in bowel motility, they may also be beneficial to bone health.

Impact of Blood pH
Other research from Tufts University Bone Metabolism Laboratory has considered how the body’s acid-base balance may influence bone health. As food is digested, absorbed, and metabolized, some of it releases hydrogen ions (H+), which increase blood acidity. With the need to maintain a constant pH balance, this rise of H+ levels in the blood stimulates a receptor on the bone to trigger resorption, releasing alkaline compounds and calcium into the blood. Thus, bone breakdown helps to neutralize the acid pH but weakens the bone.

Research by the Tufts team found that adding bicarbonate to the diet reduced markers of bone resorption compared with a placebo, suggesting that a diet containing alkaline compounds could be beneficial to bone health.22 Fruits—even citrus—and vegetables add alkaline compounds to the body, whereas protein and grains add acidic compounds, although dietary protein shouldn’t be restricted at all, as it’s important to bone and muscle health, especially with aging. Rather, the researchers suggest reducing grain intake, especially refined grains, and replacing them with fruits and vegetables. Americans eat twice the recommended amounts of grains, specifically refined grains, while fruit and vegetable intake is well below recommendations.5 Protein is important, accounting for approximately 50% of bone volume. Amino acids are modified to facilitate the cross-linking of collagen molecules in bone. Protein also raises levels of insulin growth factor-1 that stimulates bone growth and increases calcium and phosphorus absorption in the intestine. Dietary protein intake can vary from about 0.8 to 1.5 g/kg bodyweight/day. Higher intakes of dietary protein in older people with osteoporosis is associated with higher BMD.3

Food for Thought
Although most older adults understand the increased risk for developing osteoporosis, fewer are aware of the benefits of nutrition. Given the high and rising risk of osteoporosis among the aging population and overall low consumption of calcium, vitamin D, and phytochemicals among Americans, dietary intervention is imperative. If a healthy dietary pattern is consumed, calcium from food can meet recommendations. However, vitamin D recommendations are more difficult to achieve from natural food sources through diet alone, requiring fortified food and beverages. In many cases, especially when sunlight exposure is limited, taking a vitamin D supplement is indicated. Regardless, patients should be encouraged to attain the RDAs for both calcium and vitamin D by eating a wide variety of nutrient-dense foods, especially low-fat dairy foods, seafood, and fortified foods.

Whether helping patients to prevent risk of osteoporosis, or fractures for those with the disease, both primary and geriatric practices are well-served when a registered dietitian nutritionist is engaged as part of the health care team. At a minimum, older patients should be provided nutrition education resources to support improved dietary practices. The professionals tab on the National Osteoporosis Foundation website offers excellent resources for nutrition patient education. Maximizing the nutrient density of the diet with adequate food sources of calcium, vitamin D, phytochemicals, and protein can be an effective strategy for preventing and treating osteoporosis.

— KC Wright, MS, RDN, is a research dietitian, food and nutrition writer, and advocate for healthful and sustainable food. She can be found at wildberrycommunications.com.

References
1. Osteoporosis. National Institutes of Health Osteoporosis and Related Bone Diseases National Resource Center website. https://www.bones.nih.gov/health-info/bone/osteoporosis. Accessed January 21, 2021.

2. Cosman F, de Beur SJ, LeBoff MS, et al. Clinician’s guide to prevention and treatment of osteoporosis. Osteoporos Int. 2014;25(10):2359-2381.

3. Rizzoli R, Bischoff-Ferrai H, Dawson-Hughes B, Weaver C. Nutrition and bone health in women after menopause. Womens Health. 2014;10(6):599-608.

4. Fulgoni VL, Keast DR, Bailey RL, Dwyer J. Foods, forticants, and supplements: where do Americans get their nutrients? J Nutr. 2011;141(10):1847-1854.

5. US Department of Agriculture; US Department of Health and Human Services. Dietary Guidelines for Americans 2020–2025. https://www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_Americans_2020-2025.pdf. Published December 2020.

6. Yao P, Bennett D, Mafham M, et al. Vitamin D and calcium for the prevention of fracture: a systematic review and meta-analysis. JAMA Netw Open. 2019;2(12):e1917789.

7. Kopecky SL, Bauer DC, Gulati M, et al. Lack of evidence linking calcium with or without vitamin D supplementation to cardiovascular disease in generally healthy adults: a clinical guideline from the National Osteoporosis Foundation and the American Society for Preventive Cardiology. Ann Int Med. 2016;165(12):867-868.

8. Calcium. Harvard T.H. Chan School of Public Health website. https://www.hsph.harvard.edu/nutritionsource/calcium/. Accessed January 30, 2021.

9. Calcium fact sheet for health professionals. National Institutes of Health Office of Dietary Supplements website. https://ods.od.nih.gov/factsheets/Calcium-HealthProfessional/#en1. Updated March 26, 2020. Accessed January 21, 2021.

10. Cooperman T. Which vitamins and minerals should be taken together or separately? ConsumerLab.com website. https://www.consumerlab.com/answers/which-vitamins-and-minerals-should-be-taken-together-or-separately/how-to-take-vitamins/. Updated October 10, 2019. Accessed January 21. 2021.

11. Trang HM, Cole DE, Rubin LA, Pierratos A, Siu S, Vieth R. Evidence that vitamin D3 increases serum 25-hydroxyvitamin D more efficiently than does vitamin D2. Am J Clin Nutr. 1998;68(4):854-858.

12. Tang BM, Eslick GD, Nowson C, Smith C, Bensoussan A. Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis. Lancet. 2007;370(9588):657-666.

13. Vitamin D, calcium, or combined supplementation for the primary prevention of fractures in community-dwelling adults. US Preventive Services Task Force Recommendation Statement. JAMA. 2018;319(15):1592-1599.

14. Wallace TC. Dried plums, prunes and bone health: a comprehensive review. Nutrients. 2017;9:401-421.

15. Kong SH, Kim JH, Hong AR, Lee JH, Kim SW, Shin CS. Dietary potassium intake is beneficial to bone health in a low calcium intake population: the Korean National Health and Nutrition Examination Survey (KNHANES) (2008-2011). Osteoporos Int. 2017;28(5):1577-1585.

16. Akbari S, Rasouli-Ghahroudi AA. Vitamin K and bone metabolism: a review of the latest evidence in preclinical studies. Biomed Res Int. 2018;2018:4629383.

17. Boron fact sheet for health professionals. National Institutes of Health Office of Dietary Supplements website. https://ods.od.nih.gov/factsheets/Boron-HealthProfessional/. Updated June 3, 2020. Accessed January 21, 2021.

18. Arjmandi BH, Johnson SA, Pourafshar S, et al. Bone-protective effects of dried plum in postmenopausal women: efficacy and possible mechanisms. Nutrients. 2017;9(5):496.

19. Donovan JL, Meyer AS, Waterhouse AL. Phenolic composition and antioxidant activity of prunes and prune juice (Prunus domestica). J Agric Food Chem. 1998;46:1247-1252.

20. Hooshmand S, Kern M, Metti D, et al. The effect of two doses of dried plum on bone density and bone biomarkers in osteopenic postmenopausal women: a randomized, controlled trial. Osteoporos Int. 2016;27(7):2271-2279.

21. Brown PE. Role of commodity boards in advancing the understanding of the health benefits of whole foods. Nutr Today. 2017;52(1):19Y25.

22. How diet impacts bone health. Tufts University Health & Nutrition Letter website. https://www.nutritionletter.tufts.edu/healthy-eating/how-diet-impacts-bone-health. Updated July 27, 2020. Accessed January 28, 2021.