Nutritional influences on osteoporosis

Townsend Letter for Doctors and Patients, June, 2006 by Tori Hudson

Numerous modifiable and non-modifiable factors influence the prevention or likelihood of developing osteoporosis. This review article is intended to provide the practitioner with an understanding of the nutritional influences, both dietary and supplementation, on bone density and fractures. By educating patients and especially young girls, we can hope to reduce the risk and incidence of osteoporosis and the often debilitating fractures associated with it. For women who have already been diagnosed with osteoporosis, these nutritional influences should be considered an adjunct to conventional proven therapies to slow bone loss and, more importantly, reduce the risk of fractures.

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Interventions for treating osteoporosis include both antiresorptive agents and agents that enhance bone formation. Antiresorptive agents reduce the imbalance between bone resorption and formation by decreasing excessive osteoclast activity. These agents exert their greatest effect on trabecular bone, stabilizing its structure, and thereby reducing the risk of fracture. These agents are therefore most effective at the most common site of osteoporotic fracture, the spine. Bone-forming agents enhance the number of bone-forming units and increase the activity of individual osteoblasts.

Dietary Influences

Basic sound nutrition is an essential component for normal growth and development of all tissues, including bone. Calcium intake is the nutrient considered to be the most important for attaining peak bone mass and for preventing osteoporosis. Diets that are low in calcium are those that restrict intake of dairy products, contain low amounts of fruits and vegetables, and include a high intake of calcium-poor beverages.

Although less critical than the inclusion of calcium, several other dietary factors affect bone health and can be involved in the development of low bone density. A high-sugar diet may reduce the calcium content of bone. Sugar also causes a significant increase in the fasting serum cortisol levels, and an excess of corticosteroids can cause osteoporosis. Refined grains and flours may also play a role in the development of osteoporosis. Because refined grains and flours lack nutrient-rich germ and bran, they present a significant loss of vitamins and minerals in comparison with whole grains and unrefined flour. White flour has a loss of B6, folic acid, calcium, magnesium, manganese, copper, and zinc due to the refining process. Each of those missing factors plays at least some role in bone health. Caffeine may contribute negatively to bone density by affecting calcium loss. Studies have shown an increase in calcium excretion in the urine after ingestion of caffeine. (1-3) However, this result has not been consistent in all studies. Data was collected in 138 women at two points, separated by two years. Analyses indicated no association between dietary caffeine intake and total body or femoral neck bone density or bone mass. In addition, no associations were found between caffeine consumption and longitudinal changes in total body or femoral neck bone measurements. (4)

The influence of alcohol on bone density and fractures is confusing and contradictory. Several studies have showed that chronic alcoholism leads to osteopenia and increased incidence of skeletal fractures. (5-7) Although the mechanism is not entirely clear, chronic alcoholism may have a direct effect on bone cells and/or an indirect effect through mineral regulatory hormones. However, the effect of alcohol consumption on bone resorption has still not been clearly established. Some studies show increased bone resorption in moderate and heavy drinkers, (8) whereas others have found no effect. (9) Moderate alcohol intake (>28.6 g/wk) has even been associated with higher bone mineral density in postmenopausal elderly women. (10) This may be due to lower parathyroid hormone concentrations and higher serum estradiol, both influenced by the alcohol intake. Consumption of moderate or greater amounts alcohol is also a known risk factor for osteoporosis. (11)

Several other dietary factors can influence calcium balance. Dark green leafy vegetables contain calcium that can contribute to the total day's dietary intake. Excessive dietary protein may promote bone loss. Animal protein particularly causes an increase in urinary excretion of calcium. Calcium is mobilized from the bone to buffer the acidic breakdown products of protein. In addition, the amino acid methionine is converted to homocysteine, which can also cause bone loss. Many high-protein foods also contain high amounts of phosphorus. This high phosphorus content again mobilizes calcium from the bones to maintain homeostasis in the blood stream. High phosphorus beverages are also therefore implicated in osteoporosis development. A study in children demonstrated a severe impact of soft drinks on calcium levels. Fifty-seven children with low blood calcium levels were compared to 171 children with normal calcium levels. (12) Of the 57 children who had low blood calcium levels, 66.7% drank more than four 12 to 16 ounce bottle of soft drinks per week. Only 28% of the 171 children with normal serum calcium levels consumed that many soft drinks per week. For all 228 children, a strong correlation was seen in the serum calcium level and the number of bottles of soft drinks consumed each week. The more soft drinks consumed, the lower the calcium level in the blood. High sodium diets can also cause an increase in urinary excretion of calcium in some individuals. (13)

Soy foods have received increasing attention as a food that may have a positive effect on bone health. Soybeans contain phytoestrogens called isoflavones and a particular isoflavone called daidzein. Daidzein is similar in shape to a drug called Ipriflavone, which is used in Europe to treat osteoporosis. Soy is the only dietary source of daidzein that is a non-steroidal, estrogen-like molecule. Soy also increases the menstrual cycle length by one to five days, especially the follicular phase. This may have a positive effect on bone density due to longer exposure to elevated estrogen levels.