Pumpkin seeds have long been valued as a source of the mineral zinc, and the World Health Organization recommends their consumption as a good way of obtaining this nutrient. More on the Health Benefits of Pumpkin Seeds.
Osteoporosis, a condition in which minerals and other substances are lost from the bones causing them to become thinner, more porous, and more easily broken, affects about 20-25 million Americans, primarily older women. While many people believe that consuming dairy products is a required nutritional strategy for preventing osteoporosis, the truth is that this is not necessarily true. There are many plant foods that not only contain calcium but other valuable bone-health promoting nutrients that can play a valuable role in a diet aimed at preventing osteoporosis.
Inadequate calcium intake definitely increases risk of osteoporosis. Too little calcium causes the parathyroid hormone to stimulate certain bone cells, called osteoclasts, into breaking down bone in order to raise calcium levels in the blood. Just as calcium deficiency increases risk of osteoporosis, calcium supplementation has been shown to help prevent it by increasing bone density. For example, studies have shown that supplementing with calcium increases bone density in perimenopausal women and slows bone degeneration in postmenopausal women by an average of 30-50%. These effects translate into a significant reduction in hip fractures.
Because a glass of cow's milk contains about 300 milligrams of calcium, (and the Adequate Intake level for a middle-aged adult is 1,000 milligrams), cow's milk has traditionally been marketed as a high-calcium, osteoporosis-preventing food. However, calcium is not the only nutrient involved with osteoporosis risk. Many nutrients are involved in the determination of a person's risk of osteoporosis.
The relationship between protein intake and osteoporosis is the subject of ongoing debate in scientific studies. However, it appears that under certain circumstances and at least in certain age-related groups, excess protein intake can increase a person's risk of bone mineral loss. This relationship appears to hold true particularly under circumstances in which a higher level of sulfur-containing amino acids are included in the dietary protein and when this type of diet is being consumed by older individuals. The connection between dietary protein and bone mineral loss involves pH levels in the bone tissue and sensitivity of bone cells and bone cell enzymes to changes in pH (degree of acidity).
The bone cells that help remodel bone by removing its core minerals are called osteoclasts. The activity of these cells is switched on as acidity increases. When acidity has decreased all the way to a pH level of 7.4, the removal of mineral from bone by osteoclasts can sometimes be shut down entirely. The reverse is true for osteoblasts—cells that deposit more minerals into the bone matrix and help to form new bone. In very low pH environments (highly acidic), these bone-forming cells are greatly inhibited in their activities. For both of these reasons—altered osteoclast and osteoblast activity—higher pH environments (slightly alkaline) favor retention of bone mass.
The exact way in which high-protein diets can change pH levels in different body tissues has yet to be clarified in research studies. What has been shown in numerous studies is the tendency of a high-protein diet to increase excretion of acids in the urine along with excretion of calcium. Since increased elimination of acid typically corresponds to some form of acid excess in the body, and since acid excess (low pH) in bone tissue favors loss of calcium from bone, a connection between higher protein diets, pH changes in bone tissue, and potentially unwanted loss of calcium from the bone seems likely.
Some clinical research studies can be used to help give us a sense of how this connection might work in practical terms. For example, in one study, an increase in daily protein intake from 47 to 142 grams was found to double the excretion of calcium in the urine. What might this level of protein intake look like in terms of food choices? One glass of cow's milk contains about 8 grams of protein. Three glasses of cow's milk, which would provide very close to a day's worth of calcium, would also provide 24 grams of protein. By itself, this amount would not be enough to cause problematic amounts of calcium to be removed from bone. However, in combination with other protein sources, for example, an 8-ounce chicken breast, which would contain about 56 grams of protein, and a quarter-pound hamburger (which would add another 28 grams), the day's total would be about 108 grams—much closer to the amount in the research study that doubled calcium excretion in the urine and increased risk of osteoporosis.
Another example of a nutrient that plays a role in osteoporosis is magnesium, a mineral that appears to be nearly as important as calcium in preventing problems associated with this condition. Women with osteoporosis have low bone magnesium content and other signs of magnesium deficiency, and a two-year study of magnesium supplementation in postmenopausal women has found that those receiving magnesium had a slight improvement in bone density while those receiving the placebo lost some of their bone density.
Inadequate consumption of magnesium has also been shown to decrease blood concentrations of the most active form of vitamin D (called D3). In clinical research studies, vitamin D3 has been shown to stimulate the absorption of calcium, increase bone mineral density, and reduce the risk of hip fracture. Magnesium is also required to regulate the body's levels of parathyroid hormone and calcitonin, two hormones that maintain the proper concentration of calcium in the blood.
Yet, cow's milk, which is a very good source of calcium, is not a very good source of magnesium. One cup of cow's milk only provides about 33 milligrams or about 10% of the daily requirement for a middle-aged woman.
We could add a long list of nutrients to calcium, protein, and magnesium that influence the risk of osteoporosis. Other bone-health promoting nutrients include vitamin D, boron, vitamin K, vitamin C, ipriflavone, silicon, and vitamins B6, B12, and folate. Not only is cow's milk less than ideal as food source of these nutrients, but in some cases (like vitamin C) it is nearly devoid of the nutrient altogether.
Could you get enough of all nutrients - including calcium - without consuming cow's milk, or cow's milk yogurt, or cow's milk cheese? The answer is definitely "yes." In fact, most women in the world as a whole who do not develop osteoporosis also do not consume dairy products. The foods they eat, including the World's Healthiest Foods, are concentrated in calcium and other of the bone-health promoting nutrients noted above. Just how could you get enough calcium without consuming dairy products? Consider the example below involving a dairy-free salad.
As previously described, calcium is a mineral found in a wide variety of foods besides dairy products. Virtually all greens contain calcium. By "greens," we mean all the dark green leafy vegetables like spinach, chard, mustard greens and collard greens, as well as lettuces, like romaine. Shredded cabbage is also a source of calcium.
Virtually all nuts and seeds - and especially sesame seeds - contain calcium. So do most beans, including navy, pinto, kidney, and black are all calcium-containing foods. Additionally, tofu can also be an important source of calcium, particularly when the tofu has been calcium-precipitated (meaning that calcium was used to help convert the soy milk into tofu) it can provide a significant amount of calcium.
Although none of the above non-dairy foods, all by itself, will provide a large percent of your total day's calcium, when these foods are combined, the total calcium they provide is actually higher than the amount in an 8-ounce glass of cow's milk. Let's take a salad as our example. Romaine lettuce contains 20 milligrams of calcium per cup. Using 2 cups of romaine as our salad base, we start off with 40 milligrams of calcium. A half-cup of chard leaves would bump us up another 25 milligrams, to 65 total. Adding one-half cup of soybeans we jump up 87 milligrams to 152 while sprinkling on 2 tablespoons of sesame seeds brings us up to 237 milligrams. To top it off, add one-third of a cup of kidney beans and we have a salad that provides a substantial 277 milligrams of calcium.
How does this amount compare to a glass of 2% cow's milk? In terms of total calcium, it's very similar! A glass of 2% has about 285-300 milligrams. And while it is true that our salad contains nearly twice as many calories as an 8-ounce glass of 2% cow's milk, it also contains a much wider variety of nutrients. These nutrients include fiber, which is absent in the cow's milk altogether, and vitamin C, which is over 10 times more plentiful in the romaine lettuce alone than in a cup of 2% milk.
As the salad above highlights, since many of the World's Healthiest Foods contain calcium and other important bone-promoting nutrients, we feel that meal plans concentrated in these foods may help reduce risk of osteoporosis as effectively, or even more effectively, than cow's milk. While Table 1 below gives details on the calcium content of some of the World's Healthiest Foods, the article on our website about Osteoporosis goes into more detail about the condition itself as well as nutrients necessary for promoting bone health. It gives detailed examples of foods other than dairy products as well as recommended dietary suggestions that can help you to promote bone health.
| Food | Serving | Calcium (mg) | % DV | Density | Quality |
|---|---|---|---|---|---|
| Sesame seeds | 0.25 cup | 351.0 | 35.1 | 3.1 | Good |
| Collard greens, boiled | 1.0 cup | 226.1 | 22.6 | 8.2 | Excellent |
| Turnip greens, cooked | 1.0 cup | 197.3 | 19.7 | 12.3 | Excellent |
| Soybeans, cooked | 1.0 cup | 175.4 | 17.5 | 1.1 | - |
| Navy beans, cooked | 1.0 cup | 127.4 | 12.7 | 0.9 | - |
| Mustard greens, boiled | 1.0 cup | 103.6 | 10.4 | 8.9 | - |
| Chard, boiled | 1.0 cup | 101.5 | 10.2 | 5.2 | Very good |
| Kale, fresh, boiled | 1.0 cup | 93.6 | 9.4 | 4.6 | Very good |
| Almonds | 0.25 cup | 91.8 | 9.2 | 0.8 | - |
| Tofu, raw | 4.0 oz-wt | 86.2 | 10.0 | 2.1 | Good |
| Pinto beans, cooked | 1.0 cup | 82.1 | 8.2 | 0.6 | - |
| Garbanzo beans, cooked | 1.0 cup | 80.4 | 8.0 | 0.5 | - |
| Green snap/string beans, boiled | 1.0 cup | 57.5 | 5.8 | 2.4 | Good |
| Celery, raw | 1.0 cup | 48.0 | 4.8 | 4.5 | Good |
| Black beans, boiled | 1.0 cup | 46.4 | 4.6 | 0.4 | - |
| Cabbage, raw | 1.0 cup | 41.8 | 4.2 | 2.5 | Good |
| Lettuce, romaine | 2.0 cup | 40.3 | 4.0 | 4.6 | Good |
Dawson-Hughes B, Harris SS, Rasmussen H, Song L, Dallal GE. Effect of dietary protein supplements on calcium excretion in healthy older men and women. J Clin Endocrinol Metab 2004 Mar;89(3):1169-73.
Ince BA, Anderson EJ, Neer RM. Lowering dietary protein to U.S. Recommended dietary allowance levels reduces urinary calcium excretion and bone resorption in young women. J Clin Endocrinol Metab 2004 Aug;89(8):3801-7.
Itoh R, Nishiyama N, Suyama Y. Dietary protein intake and urinary excretion of calcium: a cross-sectional study in a healthy Japanese population. Am J Clin Nutr 1998 Mar;67(3):438-44.
Lemann J Jr. Relationship between urinary calcium and net acid excretion as determined by dietary protein and potassium: a review. Nephron 1999;81 Suppl 1:18-25.
Pannemans DL, Schaafsma G, Westerterp KR. Calcium excretion, apparent calcium absorption and calcium balance in young and elderly subjects: influence of protein intake. Br J Nutr 1997 May;77(5):721-9.
Arnett TR. Extracellular pH regulates bone cell function. J Nutr 2008 Feb;138(2):415S-8S.
Blomqvist R. Importance for pH control of osteoclasts in bone resorption. Duodecim 2006;122(4):477-8.
Kohn DH, Sarmadi M, Helman JI, Krebsbach PH. Effects of pH on human bone marrow stromal cells in vitro: implications for tissue engineering of bone. J Biomed Mater Res 2002 May;60(2):292-9.
Meghji S, Morrison MS, Henderson B, Arnett TR. pH dependence of bone resorption: mouse calvarial osteoclasts are activated by acidosis. Am J Physiol Endocrinol Metab 2001 Jan;280(1):E112-9.
Muzylak M, Arnett TR, Price JS, Horton MA. The in vitro effect of pH on osteoclasts and bone resorption in the cat: implications for the pathogenesis of FORL. J Cell Physiol 2007 Oct;213(1):144-50.
Tennant GB, Truran LN, Bailey-Wood R, Burnett AK. Control of pH in human long-term bone marrow cultures with low-glucose medium containing zwitterion buffer lengthens the period of haemopoietic activity. Br J Haematol 2000 Jun;109(4):785-7.
Agnusdei D, Crepaldi G, Isaia G, et al. A double blind, placebo-controlled trial of ipriflavone for prevention of postmenopausal spinal bone loss. Calcif Tissue Int 1997; 61: 142-147.
Brattstrom LE, Hultberg BL, Hardebo JE. Folic acid responsive postmenopausal homocysteinemia. Metabolism 1985; 34: 1073-1077.
Chestnut CH 3rd, Bell NH, Clark GS, et al. Hormone replacement therapy in postmenopausal women: urinary N-telopeptide of type I collagen monitors therapeutic effect and predicts response of bone mineral density. Am J Med 1997; 102: 29-37.
Eaton-Evans J. Osteoporosis and the role of diet. Br J Biomedical Sci 1994; 51: 358-370.
Ellis F, Holesh S, Ellis J. Incidence of osteoporosis in vegetarians and omnivores. Am J Clin Nutr 1972; 25: 55-58.
Lore F, Nuti R, Vattimo A, Caniggia A. Vitamin D metabolites in postmenopausal osteoporosis. Horm Metabol Res 1984; 16: 58.
Recker R. Calcium absorption and achlorhydria. New Engl J Med 1985; 313: 70-73 61: 391-393.
Saltman PD, Strause LG. Strause LG. The role of trace minerals in osteoporosis. J Am Coll Nutr 1993; 4: 384-389.
Vermeer C, Gijsbers BL, Cracium AM, et al. Effects of vitamin K on bone mass and bone metabolism. J Nutr 1996; 126: 1187S-1191S.
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