Protein Intake and Bone Loss and Bone Fractures - Term Paper Example

Introduction Research has shown that intake of adequate protein in the diet may be beneficial to bone health; however its exact role is still controversial. This essay examines the role of protein in bone loss/bone fractures. Many studies have described the positive role of protein in bone health. Promislow et al., 2002 did a prospective study in the elderly, studying the associations of total, animal, and vegetable protein with bone mineral density (BMD) and the variations in these associations with calcium intake. A positive association was shown between animal protein consumption, and an increase in bone mineral density (BMD), which was more significant in women. However, a negative association was noted between vegetable protein and BMD, in both sexes. Avenell & Handoll, 2003 conducted a systematic review of randomized and quasi-randomized trials in patients aged 65 years or more, to evaluate whether protein and energy supplementation could influence the recovery after hip fracture. The limited evidence (three trials) showed that oral protein and energy supplements may reduce an unfavorable outcome (Avenell & Handoll, 2003.) Sellmeyer et al., 2001 did a prospective cohort study in women aged more than 65 years, over a period of years. The density of the hip bones was measured. The results confirmed the hypothesis that an increased intake of vegetable protein along with a reduced intake of animal protein reduces the nutrition-induced acidification. This preserves the body’s protein reserves, prevents bone loss, and thus, reduces the risk of hip fracture in the elderly. Munger, Cerhan, Chiu, 1999 evaluated the relation between protein intake and other nutrients and the incidence of hip fracture in women aged 55–69 years. The study concluded that protein intake (especially animal protein) might be associated with a reduced incidence of hip fractures. Hannan et al., 2000 conducted the population-based Framingham Osteoporosis study, which examined the relation between protein intake and subsequent 4-year change in bone mineral density (BMD). The results showed that a lower protein intake was associated with significant bone loss at femoral and spine sites, especially when associated with a lower percent intake of animal protein. The study concluded that protein intake is important in maintaining bone or minimizing bone loss in elderly persons, and that a higher intake of animal protein does not appear to affect bone health in the elderly. In a similar study, Rapuri, Gallagher, Haynatzka, 2003 studied the associations of dietary protein intake with baseline bone mineral density (BMD) and the rate of bone loss over 3 years in postmenopausal elderly women. In addition, they also examined the effect of dietary calcium intake with protein intake on BMD. The results revealed that a higher intake of protein was associated with higher BMD, especially in women with calcium intakes > 408 mg/d. There was no association seen between protein intake and the rate of bone loss. There is an increased excretion of calcium from the body as the dietary protein intake increases (Heaney, 2002; Heaney, 1998). However, provided that the dietary calcium-to-protein ratio is >20:1 (mg:g), there will not be any harm to bone health (Heaney, 1998). There is also a perception that both protein and phosphorus can cause calcium loss. However, studies have shown that complex dietary proteins (with a high phosphorus content), do not cause calcium loss, and there are no adverse effects on calcium metabolism provided there is a phosphorus intake of up to 2000 mg/d (Spencer, Kramer, Osis, 1998). Conversely, a diet low in protein and phosphorus may have adverse effects on calcium balance in the elderly. It can be therefore said that in the elderly, a normal protein intake along with normal/relatively high phosphorus and calcium intake could be protective (Spencer, Kramer, Osis, 1998.) Osteoporotic fractures can result from malnutrition, probably due to a low IGF-I (somatomedin system) level. Protein supplements along with adequate intake of vitamin D and calcium increases circulating IGF-I levels, improves clinical outcomes after hip fracture, and prevents BMD loss at the proximal femur (Rizzoli et al., 2001). However, the use of biochemical markers in the acute postoperative period in the assessment of nutritional status is not recommended (Bachrach-Lindstrum et al., 2001.) Another study by Dawson-Hughes & Harris, 2002 showed a favorable effect on BMD in elderly by increasing the protein intake along with supplementation of calcium citrate malate and vitamin D (Dawson-Hughes & Harris, 2002). There is also a debate on whether plant protein is less detrimental than animal protein. However, it is important to note that it is the total diet that determines the effect on bone. Any adverse effects of protein can be countered by adequate intake of calcium (form milk, fruits and vegetables) (Massey, 1998.) Some studies mention about the harmful effects of dietary protein on bone health. An excess amount of protein from foods with high renal acid load potential can affect bone health adversely (Barzel & Massey, 1998; Massey, 2003). In order to counter this effect it is necessary to consume alkali rich foods (chemical salts or dietary fruits and vegetables high in potassium) or supplements (Barzel & Massey, 1998.) The Harvard Nurses Health study examined the role of milk consumption in osteoporotic fractures. The study concluded that there is no protective effect conferred by milk on osteoporotic fractures, and that a moderate consumption of animal food might play a protective role against hip fracture (Butler). Feskanich et al., 1996, conducted a prospective study, which revealed that an increased risk of forearm fracture was associated with women who consumed more than 95 g protein per day compared with less than 68 g per day. A significantly increased risk of forearm fracture was also seen in women who consumed five or more servings of red meat per week. A few studies have described the role of other factors in bone health. Welteh et al., 1995 conducted a meta-analysis. The study concluded that in order to optimize bone mass before the onset of menopause, the intake of calcium should at least be as high 800 mg/d. Elderly men have low levels of both bioavailable estrogen (E) and bioavailable testosterone (T). In both genders, estrogen deficiency increases bone resorption as well as negatively impact the compensatory increase in bone formation (Riggs, Khosla, Melton, 1998). According to the population study, Framingham Osteoporosis Study, the use of estrogen may maintain bone health in women, while in men, smoking was associated with bone loss (Hannan et al., 2000). The study by Freudenheim, Johnson, Smith, 2000 indicates that high levels of intake of energy, protein, calcium, phosphorus, zinc, and folate were associated with slower bone loss. A high intakes of caffeine ( >300 mg/d) could speed up spinal bone loss in elderly postmenopausal women (Rapuri et al., 2001.) Yano et al., 1985 studied the association between intake of milk, calcium, and vitamin D and bone mineral content (BMC) in the elderly. A positive association was noted, although the results were not consistent. Ilich, Brownbill, Tamborini, 2003 performed a cross-sectional study in 136 postmenopausal women with the intention of noting the association between different nutrients and bone mass in various parts of the body. The measurements, which were performed included: lean and fat tissue assessment, bone mineral density, dietary intake (including supplements), serum parathyroid hormone and vitamin D. The results suggested an association between BMD and the nutrients magnesium, vitamin C, zinc, protein, energy, and calcium. However, the exact role of these nutrients and their relevance to bone health has to be studied further and the role of any single nutrient on bone mass is yet to be known. Tucker et al., 2002 studied the association between dietary patterns and BMD in the elderly. Six dietary patterns were studied, which included: meat and sweet baked products; meat, dairy, and bread; sweet baked products; alcohol; candy; and fruit, vegetables, and cereal. The results indicated that a high fruit and vegetable intake had a protective role in men, while in both men and women a high candy consumption was associated with low BMD. Barker et al., 2005 performed a case control study in elderly women to know if excessive vitamin A exposure (multivitamin or cod liver oil supplementation) could increase the risk of fracture. They concluded that there was no such risk. For good bone health in the elderly, regular exercise is beneficial and improves the functional capacity (Evans & Cyr-Campbell, D, 1997). Although a plant-based diet can provide calcium, the amount provided may not be sufficient, and therefore, fortified foods or supplements are also required (Weaver, Proulx, Heaney, 1999.) Conclusion Many studies have shown a positive influence of dietary protein intake on bone mineral density (BMD), while other studies have shown a harmful effect. However, it is known that there is an increased excretion of calcium from the body as the dietary protein intake increases, although this harmful effect can be minimized with adequate intake of calcium in the diet (the intake of calcium should at least be as high 800 mg/d.) There is currently no clear agreement on the effect of dietary protein intake on bone, but there is some indication that a low calcium intake could adversely influence the effect of dietary protein on fracture risk. On the specific issue of whether animal protein is better than plant protein in bone health, it is still controversial. While some studies have shown a positive association between animal protein consumption, and an increase in bone mineral density (BMD), and a negative association between vegetable protein and BMD, other studies have shown that an increased intake of vegetable protein along with a reduced intake of animal protein prevents bone loss. 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The relationship between diet and bone mineral content of multiple skeletal sites in elderly Japanese-American men and women living in Hawaii. Am J Clin Nutr. 877-888. Read More