August 2013 Issue

Plant-Based Foods and Osteoporosis — Tell Clients About Other Bone-Building Nutrients While Helping Them Plan Meals
By Densie Webb, PhD, RD
Today’s Dietitian
Vol. 15 No. 8 P. 16

As nutrition professionals, you often tell clients and patients the two most important dietary recommendations for bone health: Get plenty of calcium and lots of vitamin D. Dairy products are the primary source for both of these nutrients. Other bone builders, such as high-quality protein and zinc, are abundant in red meat. So where does that leave vegetarians, who may not consume dairy products or eat meat? And what about other less appreciated bone-building nutrients such as omega-3 fatty acids?

According to a recent Gallup Poll, about 5% of Americans identify themselves as vegetarian. Some research has suggested that osteoporosis, the thinning of bones that worsens with age and increases the risk of bone fractures, is more common among vegetarians than meat eaters and more common still among vegans, who don’t eat animal products at all. However, it’s also been suggested that the increased risk of osteoporosis among vegetarians, if it truly exists, isn’t clinically significant.1

Recent information from the National Osteoporosis Foundation indicates that 9 million adults in the United States have osteoporosis, and 48 million experience low bone mass that puts them at increased risk of broken bones. It isn’t known how many of these people are vegetarians. Yet because vegetarian diets vary widely (some include eggs, dairy, fish, and/or chicken), it’s difficult to determine their impact on bone health for each person.

Regardless of how your clients and patients define their vegetarian diets, it’s important to keep in mind the potential for low intakes of some vital bone-building nutrients when helping them plan their meals.

Calcium
No one questions that calcium is an important mineral for bone, as 99% of the calcium in the body is found in bone. The Recommended Dietary Allowance (RDA) for calcium is 1,000 mg/day for women up to age 50 and men up to age 70, and 1,200 mg/day for anyone older, which is a level that’s difficult for both vegetarians and nonvegetarians to reach. According to National Health and Nutrition Examination Survey 2005-2006 data, more than 50% of the American population has inadequate calcium intakes. If calcium-rich dairy foods aren’t part of the diet, it becomes difficult to meet the RDA.

According to Katherine Tucker, PhD, a professor of health science at Northeastern University in Boston, vegetarians who don’t consume dairy and depend mainly on plant sources for calcium may have higher calcium requirements. That’s because calcium absorption may be affected by higher levels of phytates, oxalates, and fiber in calcium-rich plant foods such as leafy-green vegetables and legumes.

Tucker also notes that calcium found naturally in foods such as milk, yogurt, and cheese may be used more efficiently than supplements and recommends that vegetarians who don’t consume dairy include foods fortified with calcium and vitamin D. In addition, research has cast doubt on calcium supplementation’s effectiveness to protect against bone fractures and has shown a possible association with cardiovascular disease and an increased risk of kidney stones.

Vitamin D
The debate about the role of vitamin D in optimal health continues, but what isn’t debated is its importance for bone health. The RDA for vitamin D is 600 IU/day for people between the ages of 1 and 70, and 800 IU for those older than 70.

Individual dietary needs can vary, however, depending on exposure to sunlight, which triggers the skin’s conversion of 7-dehydrocholesterol to vitamin D3. The skin’s ability to produce vitamin D3 diminishes with age, just as overall food intake tends to decline, including foods rich in vitamin D. Season, time of day, length of day, cloud cover, smog, skin color, and sunscreen all affect the skin’s ability to produce vitamin D.2

Vitamin D from dairy is in the form of vitamin D3. Supplements may contain either D2 or D3. While both forms are beneficial, D3 may be the more potent of the two at high doses.2 However, D2 isn’t derived from animals and may be the vitamin of choice for vegetarians.

Keep in mind that, according to the US Preventive Services Task Force, an independent and volunteer panel of national experts in prevention and evidence-based medicine, there isn’t enough evidence to determine whether vitamin D supplementation can prevent fractures, so it’s more advantageous for clients to obtain the nutrient from food. Dietary sources of vitamin D include fatty fish, egg yolks, and fortified milk as well as certain types of mushrooms exposed to UV light (in the form of vitamin D2). According to the Mushroom Council, stores currently offer various light-exposed mushrooms that provide close to 400 IU of vitamin D per serving (approximately 4 to 5 white button or cremini mushrooms or one portobello). An 8-oz glass of fortified skim milk provides about 120 IU of vitamin D3. Soy products (such as soymilk), orange juice, some yogurts, and ready-to-eat breakfast cereals commonly are fortified with calcium and sometimes vitamin D.

Other Bone-Building Nutrients
While calcium and vitamin D are widely recognized as nutrients needed for bone health, there are others less appreciated for their roles in bone health that may fall short for vegetarians.

Vitamin B12
Because B12 is found naturally only in animal foods, vegetarians, especially older vegetarians and vegans, are at risk of low intake. Ten percent to 30% of older adults are affected by atrophic gastritis, a condition in which the production of hydrochloric acid in the stomach is decreased, which results in decreased absorption of vitamin B12 from food.3 However, synthetic B12 added to fortified foods and supplements is usually well absorbed.

While B12 is best known for its role in forming red blood cells and in neurological function, some studies have found that low blood levels of B12 are associated with a lower bone density and greater risk of osteoporosis and fracture.4-7 Low blood levels of vitamin B12 also may boost homocysteine in the blood, which has been associated with a higher risk of fracture.8 Homocysteine levels typically rise with age, potentially putting older vegetarians at increased risk of osteoporosis.9 Plant sources of vitamin B12 are fortified with this vitamin and include some soy products, ready-to-eat breakfast cereals, vegetarian meat analogs, energy or snack bars, and nutritional yeast.

DHA and EPA
The omega-3 fatty acids DHA and EPA may affect bone health through various complex interactions, including improved calcium retention.10 Higher dietary ratios of omega-6 fatty acids (mainly linoleic acid from vegetable oils) to omega-3s (eg, fish, flaxseed, walnuts, canola oil, algae) may result in lower bone density.11 Consuming three servings of fatty fish per week has been found to protect against bone loss.12 However, results of studies examining the effect of fish oil on bone health haven’t been consistent.13 The omega-3s found in flax, walnuts, canola, and algae may provide similar bone benefits as from fatty fish, but they haven’t been well researched.

Still, Tucker says DHA and EPA are important because of the roles they play in managing the production of inflammatory compounds that can accelerate bone loss. Most vegetarian sources of omega-3s are in the form of alpha-linolenic acid, which is converted inefficiently to EPA and DHA in the body. Some supplements, however, provide EPA and DHA directly.

Protein
For years, conventional wisdom held that high protein intakes caused calcium to be leached from bone, resulting in loss of bone mass. However, in recent years, studies have shown that higher protein intakes actually are associated with greater bone density and lower fracture risk.

The Framingham Osteoporosis Study of older adults found that those with the highest protein intakes had the lowest rates of bone loss. Research also suggests that risk reduction is similar whether protein comes from vegetable or animal sources.14 However, according to some research, protein may be protective only when calcium intake is high.15

Zinc
Especially rich in red meat, zinc is the mineral that’s essential for bone health. Both intake and serum concentrations of zinc often are significantly lower in vegetarian diets than nonvegetarian diets.16 The zinc content of bones decreases with age and with menopause, making the mineral especially important in the diets of older vegetarians. The RDA for zinc is 11 mg/day for adult men, 8 mg/day for women, and 11 and 12 mg/day for pregnant and lactating women.

The Food and Nutrition Board of the National Academy of Science recommends that vegetarians get at least 50% more zinc than meat eaters. Fortified breakfast cereals and beans that have been soaked before cooking to minimize the effect of phytates are good sources.

Bone-Healthy Diet for Vegetarians
Before counseling your vegetarian clients and patients, it’s important to determine the foods their particular diets include or exclude. Reed Mangels, PhD, RD, LD, FADA, nutrition advisor for The Vegetarian Resource Group, says most of the potential problems with vegetarian diets and bone health are the result of poor dietary planning, not the lack of animal foods. “Anyone whose diet is too low in calcium, protein, vitamin D, or any other nutrients related to bone health is at risk.” And, she says, “Vegetarians actually may be better in some instances because their diets tend to be higher in potassium, vitamin C, and total antioxidants, all of which appear to promote bone health.”

While good nutrition is essential for bones, Vandana Sheth, RDN, CDE, a spokesperson for the Academy of Nutrition and Dietetics and lifelong vegetarian says, “You need to recognize that food is just part of the picture. Besides key nutrients there’s a list of other contributing factors, such as high sodium intake, caffeine consumption, smoking, lack of physical activity, and excessive vitamin A, that can raise risk.”

— Densie Webb, PhD, RD, is a freelance writer, editor, and industry consultant based in Austin, Texas.

 

References
1. Ho-Pham L, Nguyen N, Nguyen T. Effect of vegetarian diets on bone mineral density: a Bayesian meta-analysis. Am J Clin Nutr. 2009;90(4):943-950.

2. Dietary supplement fact sheet: vitamin D. Office of Dietary Supplements website. http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional. Reviewed June 21, 2011.

3. Dietary supplement fact sheet: vitamin B12. Office of Dietary Supplements website. http://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional. Reviewed June 24, 2011.

4. Van Wijngaarden J, Doets E, Szczecinska A, et al. Vitamin B12, folate, homocysteine, and bone health in adults and elderly people: a systematic review with meta-analyses. J Nutr Metab. 2013;2013:486186.

5. Tucker K, Hannan M, Qiao N, et al. Low plasma vitamin B12 is associated with lower BMD: the Framingham Osteoporosis Study. J Bone Miner Res. 2005;20(1):152-158.

6. Morris M, Jacques P, Selhub J. Relation between homocysteine and B-vitamin status indicators and bone mineral density in older Americans. Bone. 2005;37(2):234-242.

7. Dhonukshe-Rutten R, Lips M, de Jong N, et al. Vitamin B12 status is associated with bone mineral content and bone mineral density in frail elderly women but not in men. J Nutr. 2003;133(3):801-807.

8. McLean R, Jacques P, Selhub J, et al. Homocysteine as a predictive factor for hip fracture in older persons. N Engl J Med. 2004;350(20):2042-2049.

9. Krivosíková Z, Krajcovicová-Kudiácková M, Spustová V, et al. The association between high plasma homocysteine levels and lower bone mineral density in Slovak women: the impact of vegetarian diet. Eur J Nutr. 2010;49(3):147-153.

10. Baggio B, Budakovic A, Nassuato M, et al. Plasma phospholipid arachidonic acid content and calcium metabolism in idiopathic calcium nephrolithiasis. Kidney Int. 2000;58(3):1278-1284.

11. Weiss L, Barrett-Connor E, von Mühlen D. Ratio of n-6 to n-3 fatty acids and bone mineral density in older adults: the Rancho Bernardo Study. Am J Clin Nutr. 2005;81(4):934-938.

12. Farina E, Kiel D, Roubenoff R, et al. Protective effects of fish intake and interactive effects of long-chain polyunsaturated fatty acid intakes on hip bone mineral density in older adults: the Framingham Osteoporosis Study. Am J Clin Nutr. 2011;93:1142-1151.

13. Orchard T, Pan X, Cheek F, Ing S, Jackson R. A systematic review of omega-3 fatty acids and osteoporosis. Br J Nutr. 2012;107 Suppl 2:S253-S260.

14. Thorpe D, Knutsen S, Beeson W, Rajaram S, Fraser G. Effects of meat consumption and vegetarian diet on risk of wrist fracture over 25 years in cohort of peri- and postmenopausal women. Public Health Nutr. 2008;11(6):564-572.

15. Dawson-Hughes B, Harris S, Krall E, et al. Effect of withdrawal of calcium and vitamin D supplements on bone mass in elderly men and women. Am J Clin Nutr. 2000;72(3):745-750.

16. Foster M, Chu A, Petocz P, Samman S. Effect of vegetarian diets on zinc status: a systematic review and meta-analysis of studies in humans. J Sci Food Agric. 2013;Epub ahead of print.

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