Dietary salt, urinary calcium, and bone loss

The effect of a high-protein, high-sodium diet on calcium and bone metabolism in postmenopausal women and its interaction with vitamin D receptor genotype

The influence of a high-Na, high-protein (calciuric) diet on Ca and bone metabolism was investigated in postmenopausal women (aged 50-67 years) who were stratified by vitamin D receptor (VDR) genotype. In a crossover trial, twenty-four women were randomly assigned to a diet high in protein (90 g/d) and Na (180 mmol/d) or a diet adequate in protein (70 g/d) and low in Na (65 mmol/d) for 4 weeks, followed by crossover to the alternative dietary regimen for a further 4 weeks. Dietary Ca intake was maintained at usual intakes (about 20 mmol (800 mg)/d). Urinary Na, K, Ca, N and type I collagen cross-linked N-telopeptide (NTx; a marker of bone resorption), plasma parathyroid hormone (PTH), serum 25-hydroxycholecalciferol (25(OH)D3), 1,25-dihydroxycholecalciferol (1,25(OH)2D3), osteocalcin and bone-specific alkaline phosphatase (B-Alkphase) were measured in 24 h urine samples and fasting blood samples collected at the end of each dietary period. The calciuric diet significantly (P<0.05) increased mean urinary Na, N, K, Ca and NTx (by 19 %) compared with the basal diet, but had no effect on circulating 25(OH)D3, 1,25(OH)2D3, PTH, osteocalcin or B-Alkphase in the total group (n 24). There were no differences in serum markers or urinary minerals between the basal and calciuric diet in either VDR genotype groups. While the calciuric diet significantly increased urinary NTx (by 25.6 %, P<0.01) in the f+ VDR group (n 10; carrying one or more (f) Fok I alleles), it had no effect in the f- VDR group (n 14; not carrying any Fok I alleles). It is concluded that the Na- and protein-induced urinary Ca loss is compensated for by increased bone resorption and that this response may be influenced by VDR genotype.

The DASH diet and sodium reduction improve markers of bone turnover and calcium metabolism in adults

Dietary strategies to prevent and treat osteoporosis focus on increased intake of calcium and vitamin D. Modification of whole dietary patterns and sodium reduction may also be effective. We examined the effects of two dietary patterns and three sodium levels on bone and calcium metabolism in a randomized feeding study. A total of 186 adults, aged 23-76 y, participated. After a 2-wk run-in period, participants were assigned randomly to diets containing three levels of sodium (50, 100 and 150 mmol/d) to be consumed for 30 d in random order. Serum osteocalcin (OC), C-terminal telopeptide of type I collagen (CTX), fasting serum parathyroid hormone (PTH), urinary sodium, potassium, calcium and cAMP were measured at baseline and at the end of each sodium period. The Dietary Approaches to Stop Hypertension (DASH) diet reduced serum OC by 8-11% and CTX by 16-18% (both P < 0.001). Urinary calcium excretion did not differ between subjects that consumed the DASH and control diets. Reducing sodium from the high to the low level significantly decreased serum OC 0.6 microg/L in subjects that consumed the DASH diet, fasting serum PTH 2.66 ng/L in control subjects and urinary calcium 0.5 mmol/24 h in both groups. There were no consistent effects of the diets or sodium levels on urinary cAMP. In conclusion, the DASH diet significantly reduced bone turnover, which if sustained may improve bone mineral status. A reduced sodium intake reduced calcium excretion in both diet groups and serum OC in the DASH group. The DASH diet and reduced sodium intake may have complementary, beneficial effects on bone health.

UK Food Standards Agency Optimal Nutrition Status Workshop: environmental factors that affect bone health throughout life

The UK Food Standards Agency (FSA) convened a group of expert scientists to discuss and review UK FSA- and Department of Health-funded research on diet and bone health. This research focused on the lifestyle factors that are amenable to change and may significantly affect bone health and the risk of osteoporotic fracture. The potential benefits of fruits and vegetables, meat, Ca, vitamins D and K and phyto-oestrogens were presented and discussed. Other lifestyle factors were also discussed, particularly the effect of physical activity and possible gene-nutrient interactions affecting bone health.

Dietary animal and plant protein and human bone health: a whole foods approach

Urinary calcium excretion is strongly related to net renal acid excretion. The catabolism of dietary protein generates ammonium ion and sulfates from sulfur-containing amino acids. Bone citrate and carbonate are mobilized to neutralize these acids, so urinary calcium increases when dietary protein increases. Common plant proteins such as soy, corn, wheat and rice have similar total S per g of protein as eggs, milk and muscle from meat, poultry and fish. Therefore increasing intake of purified proteins from either animal or plant sources similarly increases urinary calcium. The effects of a protein on urinary calcium and bone metabolism are modified by other nutrients found in that protein food source. For example, the high amount of calcium in milk compensates for urinary calcium losses generated by milk protein. Similarly, the high potassium levels of plant protein foods, such as legumes and grains, will decrease urinary calcium. The hypocalciuric effect of the high phosphate associated with the amino acids of meat at least partially offsets the hypercalciuric effect of the protein. Other food and dietary constituents such as vitamin D, isoflavones in soy, caffeine and added salt also have effects on bone health. Many of these other components are considered in the potential renal acid load of a food or diet, which predicts its effect on urinary acid and thus calcium. "Excess" dietary protein from either animal or plant proteins may be detrimental to bone health, but its effect will be modified by other nutrients in the food and total diet.

Plasma amino acid concentrations in healthy and cognitively impaired oldest-old individuals: associations with anthropometric parameters of body composition and functional disability

Only a few reports exist of plasma amino acid profiles in the oldest-old, and none exist of the oldest-old with cognitive problems. Therefore, we measured fasting plasma amino acid concentrations in twenty-three healthy community-dwellers aged 90-103 years (group A); eighteen community-dwellers with mild cognitive impairment without dementia aged 91-104 years (group B); thirty-three patients with dementia aged 96-100 years (group C); and sixty healthy young controls aged 20-50 years. Biochemical and anthropometric parameters, and the basic activities of daily living (ADL) were also measured. Independent of cognitive status, in all oldest-old groups, essential:non essential amino acids (EAA:NEAA) was lower than in young controls and positively associated with body muscle mass. Patients with dementia were further characterized by a negative association between EAA:NEAA and the number of dependent ADL. All oldest-old groups had higher values of tyrosine:other large neutral amino acids (LNAA) than young controls. Groups B and C also had a higher phenylalanine:other LNAA. These data show that abnormalities in plasma amino acid profile are common in oldest-old individuals independent of their cognitive status, but that, in oldest-old patients with dementia, they are associated with functional disability. The abnormalities in phenylalanine and tyrosine plasma availability could contribute to the cause or aggravation of concurrent cognitive problems because these amino acids are neurotransmitter precursors and compete with other LNAA for transport into the brain.

Harmful effects of dietary salt in addition to hypertension

In addition to raising the blood pressure dietary salt is responsible for several other harmful effects. The most important are a number which, though independent of the arterial pressure, also harm the cardiovascular system. A high salt intake increases the mass of the left ventricle, thickens and stiffens conduit arteries and thickens and narrows resistance arteries, including the coronary and renal arteries. It also increases the number of strokes, the severity of cardiac failure and the tendency for platelets to aggregate. In renal disease, a high salt intake accelerates the rate of renal functional deterioration. Apart from its effect on the cardiovascular system dietary salt has an effect on calcium and bone metabolism, which underlies the finding that in post-menopausal women salt intake controls bone density of the upper femur and pelvis. Dietary salt controls the incidence of carcinoma of the stomach and there is some evidence which suggests that salt is associated with the severity of asthma in male asthmatic subjects.

The calciuric response to dietary salt of Dahl salt-sensitive and salt-resistant female rats

BACKGROUND

We have shown previously that the calciuric response to salt does not differ in Dahl salt-sensitive (S) and salt-resistant (R) male rats. Clinical studies with women, however, suggest an effect of salt sensitivity on the calciuric response to salt. The objective of this study was to determine whether there is an effect of salt sensitivity on the calciuric response to salt of female S and R rats.

METHOD

Dahl S and R female rats were fed high- (8%) or low- (0.3%) salt diets for 3 weeks. The rats were placed in metabolic cages for 24-hour urine collection at baseline and weekly (for sodium and calcium determination).

RESULTS

Blood pressure of female S rats was 177+/-3.0 mm Hg at week 3 of high salt intake compared with 96+/-1 mm Hg for female R rats. Female S rats excreted significantly more calcium than female R rats at baseline (P < 0.001), when fed a nonpurified diet, and during high salt intake (P = 0.004). Salt sensitivity significantly increased calcium excretion, water intake, and urine output when rats were fed a high-salt diet. Calcium excretion, water intake, and urine output of female S rats were time-dependent during high salt intake. Plasma 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D concentrations were markedly lower in female S rats fed a high-salt diet, but not in female R rats. Plasma parathyroid hormone and 1,25-dihydroxyvitamin D concentrations did not significantly differ between female S and R rats, but plasma concentrations of these two hormones at week 3 were significantly higher in S rats fed a high-salt diet compared with S rats fed a low-salt diet.

CONCLUSIONS

Our data indicate that the calciuric response to salt is greater in female S compared with female R rats, thus supporting findings on the effect of salt sensitivity reported in several clinical studies with women. The greater calciuric response to salt of female S rats compared with female R rats, which was not seen in a previous study when male S rats were compared to male R rats, suggest a gender difference in the calciuric response to salt.

The Calciuric Response to Dietary Salt of Dahl Salt-Sensitive and Salt-Resistant Male Rats

BACKGROUND

There are conflicting reports regarding the effect of salt sensitivity on the calciuric response to salt, perhaps because of gender differences and different modes of salt administration. We tested the hypothesis that the calciuric response to dietary salt would not differ for male Dahl salt-sensitive (S) and salt-resistant (R) rats.

METHOD

S and R rats were fed high- (80 g/kg) or low- (3 g/kg) salt diets for 3 weeks and urine (24 hour) was collected weekly.

RESULTS

Urinary calcium excretion was up to 20-fold greater for S and R rats fed a high-salt diet (P < 0.001) than for S and R rats fed a low-salt diet and did not differ significantly between S and R rats. S rats, however, excreted calcium in significantly higher urine volumes (P< 0.001) during high salt intake and developed hypertension. Plasma parathyroid hormone concentrations of S and R rats did not differ during low salt intake and increased significantly to the same concentration after 3 weeks of high salt intake.

CONCLUSIONS

We have previously reported that plasma 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D concentrations of male S rats, but not male R rats, were drastically reduced by 3 weeks of high salt intake. These data suggest that salt-induced hypertension and salt-induced alterations in the vitamin D endocrine system of male S rats do not affect the calciuric response to dietary salt.

Hypercalciuria

Hypercalciuria is a biological syndrome defined as excretion in the urine of more than 0.1 mmol/kg/24 hours of calcium in the absence of dietary manipulation. A number of endocrine, renal, and bone diseases can cause hypercalciuria. Urinary calcium excretion is substantially influenced by dietary intakes of calcium, sodium, protein, carbohydrates, alcohol, and potassium: a poorly balanced diet can result in hypercalciuria. Recently, there has been a burst of interest in the molecular underpinnings of rare nephrolithiasis syndromes, which have been shown to result from mutations in the CLCN5 chloride channel gene. Mutations affecting the calcium-sensing receptor (CaSR) have been identified in other forms of hypercalciuria. Idiopathic hypercalciuria is defined as hypercalciuria that persists after correction of dietary imbalances and has no detectable cause. The classification suggested by Pak ("absorptive" hypercalciuria [with three types] and "renal" hypercalciuria) is controversial and of little assistance in clinical practice. Three mechanisms can be incriminated in idiopathic hypercalciuria: increased intestinal absorption of calcium, defective reabsorption of calcium by the renal tubule, and increased bone resorption. Overexpression of the vitamin D receptor (VDR) and deficiencies in renal tubule enzymes may also be involved. Bone mineral density is moderately decreased in idiopathic hypercalciuria, particularly in the renal type. The risk of vertebral fracture seems increased, however. Overproduction of calcitriol and cytokines that stimulate bone resorption have been incriminated in the bone loss. Treatment of the cause is essential in secondary hypercalciuria (dietary advice, treatment of an underlying disease, etc.). A diet low in sodium and meat and containing no more than 800 mg of calcium per day is advocated in idiopathic hypercalciuria. Hydrochlorothiazide therapy is warranted in patients with osteopenia and an inadequate response to dietary therapy.

Calcium and vitamin D nutrition and bone disease of the elderly

Osteoporosis, a systemic skeletal disease characterized by a low bone mass, is a major public health problem in EC member states because of the high incidence of fragility fractures, especially hip and vertebral fracture. In EC member states the high incidence of osteoporotic fractures leads to considerable mortality, morbidity, reduced mobility and decreased quality of life. In 1995 the number of hip fractures in 15 countries of EC has been 382,000 and the estimated total care cost of about 9 billion of ECUs. Given the magnitude of the problem public health measures are important for preventive intervention. Skeletal bone mass is determined by a combination of endogenous (genetic, hormonal) and exogenous (nutritional, physical activity) factors. Nutrition plays an important role in bone health. The two nutrients essential for bone health are calcium and vitamin D. Reduced supplies of calcium are associated with a reduced bone mass and osteoporosis, whereas a chronic and severe vitamin D deficiency leads to osteomalacia, a metabolic bone disease characterized by a decreased mineralization of bone. Vitamin D insufficiency, the preclinical phase of vitamin D deficiency, is most commonly found in the elderly. The major causes of vitamin D deficiency and insufficiency are decreased renal hydroxylation of vitamin D, poor nutrition, scarce exposition to sunlight and a decline in the synthesis of vitamin D in the skin. The daily average calcium intake in Europe has been evaluated in the SENECA study concerning the diet of elderly people from 19 towns of 10 European countries. In about one third of subjects the dietary calcium intake results were very low, between 300 and 600 mg/day in women, and 350 and 700 mg/day in men. Calcium supplements reduce the rate of bone loss in osteoporotic patients. Some recent studies have reported a significant positive effect of calcium treatment not only on bone mass but also on fracture incidence. The SENECA study, has also shown that vitamin D insufficiency is frequent in elderly populations in Europe. There are a number of studies on the effects of vitamin D supplementation on bone loss in the elderly, showing that supplementations with daily doses of 400-800 IU of vitamin D, given alone or in combination with calcium, are able to reverse vitamin D insufficiency, to prevent bone loss and to improve bone density in the elderly. In recent years, there has been much uncertainty about the intake of calcium for various ages and physiological states. In 1998, the expert committee of the European Community in the Report on Osteoporosis-Action on prevention, has given the recommended daily dietary allowances (RDA) for calcium at all stage of life. For the elderly population, above age 65 the RDA is 700-800 mg/day. The main source of calcium in the diet are dairy products (milk, yoghurts and cheese) fish (sardines with bones), few vegetables and fruits. The optimal way to achieve adequate calcium intake is through the diet. However, when dietary sources are scarce or not well tolerated, calcium supplementation may be used. Calcium is generally well tolerated and reports of significant side-effects are rare. Adequate sunlight exposure may prevent and cure vitamin D insufficiency. However, the sunlight exposure or the ultraviolet irradiation are limited by concern about skin cancer and skin disease. The most rational approach to reducing vitamin D insufficiency is supplementation. In Europe, the RDA is 400-800 IU (10-20 microg) daily for people aged 65 years or over. This dose is safe and free of side effects. In conclusion, in Europe a low calcium intake and a suboptimal vitamin D status are very common in the elderly. Evidence supports routine supplementation for these people at risk of osteoporosis, by providing a daily intake of 700-800 mg of calcium and 400-800 IU of vitamin D. This is an effective, safe and cheap means of preventing osteoporotic fractures.

Association between urinary potassium, urinary sodium, current diet, and bone density in prepubertal children

BACKGROUND

Our understanding of the role of nutrients in bone development in children is limited.

OBJECTIVE

We examined the associations between urinary potassium, urinary sodium, usual dietary intake, and bone mineral density (BMD) in prepubertal children.

DESIGN

This was a cross-sectional study of 330 boys and girls aged 8 y. Urinary measures were assessed in a single, timed, overnight urine specimen. Usual diet was assessed with a food-frequency questionnaire completed by a parent or guardian. BMD at the femoral neck, lumbar spine, and total body was measured by dual-energy X-ray absorptiometry.

RESULTS

Urinary potassium correlated significantly with BMD at all sites (femoral neck: r = 0.20, P < 0.001; lumbar spine: r = 0.19, P = 0.001; total body: r = 0.24, P < 0.001). After adjustment for confounders (primarily lean body mass), this association was lower in magnitude but remained significant at 2 sites with a consistent trend at the third (femoral neck: P = 0.15; lumbar spine: P = 0.046; total body: P = 0.028). Urinary sodium was not associated with BMD at any site. No nutrient or food intake estimate was associated with BMD, although urinary potassium correlated significantly with potassium intake (r = 0.14, P = 0.016) and fruit and vegetable intake (r = 0.12, P = 0.033).

CONCLUSIONS

Urinary potassium was associated with both dietary intake and BMD independent of lean body mass in these well-nourished, calcium-replete young children. These findings should be confirmed in further longitudinal studies. Nevertheless, this association is likely to represent dietary intake of potassium and suggests that measurement of urinary potassium is superior to food-frequency questionnaires for assessing potassium intake in this age group.

Prevention of nephrolithiasis

The high incidence of recurrence after an initial stone event underscores the need for an effective medical prophylactic program. Dietary modification and drug therapies have long been advocated to reduce the likelihood of stone recurrence. While the efficacy of a high fluid intake has been validated in a randomized trial, the benefit of other dietary measures is based on modulation of urinary stone risk factors and outcomes derived from observational studies. Several drug therapies have been evaluated in a limited number of prospective, randomized trials and efficacy has been demonstrated for thiazides, allopurinol and alkali citrate in some populations of recurrent stone formers. The role of selective versus nonselective therapy for stone prevention awaits further study.

Acquisition of optimal bone mass in childhood and adolescence

Peak bone mass (PBM), which is achieved by early adulthood, is a key determinant of the lifetime risk of osteoporosis. Because the foundation for skeletal health is established so early in life, osteoporosis prevention begins by optimizing gains in bone mineral throughout childhood and adolescence. Heritable factors account for an estimated 60-80% of the variability in PBM, with diet, physical activity and hormonal status serving as important modifiers of bone accrual. Recent pediatric studies have clarified the tempo and magnitude of gains in bone mineral and the modulating effects of diet, activity and sex steroids. The challenge lies in designing effective means to reverse trends of decreased calcium consumption, increased sodium intake and diminished physical activity among children and adolescents. Equally important is raising the awareness of health care providers to recognize children at risk for suboptimal acquisition of PBM.

Should dietary calcium and protein be restricted in patients with nephrolithiasis?

Renal stone disease is a painful condition that affects 1-20% of the general population. Therapy aimed at decreasing the incidence of recurrent stones includes dietary advice. Dietary considerations include intake of both calcium and protein. Calcium restriction in stone formers is not recommended because it can have adverse effects on bone and the incidence of stones. Although a high-protein diet can elevate urinary calcium, uric acid, and sulfate and decrease urinary citrate, which may alter the propensity to form stones, restriction of protein to less than the current RDA for the management of stone disease can not be recommended at this time.

Review of risk factors for osteoporosis with particular reference to a possible aetiological role of dietary salt

Laboratory animal, clinical and epidemiological studies in the published literature have been reviewed in order to establish whether excessive salt intake is an important risk factor for the development of osteoporosis and whether an intervention strategy based on salt restriction would be beneficial in the prevention of osteoporosis. Genetic factors appear to be far more important than the combination of nutritional, hormonal, environmental and lifestyle factors in the pathogenesis of osteoporosis. The most important single non-genetic factor is oestrogen deficiency in postmenopausal women. Preventive measures should be aimed at maximizing peak bone mass at skeletal maturity and retarding bone loss thereafter. Apart from postmenopausal oestrogen deficiency, various factors have been incriminated as risk factors for osteoporosis, and these include age at menarche, age at and years since menopause, insufficient physical exercise, alcohol, smoking, low calcium intake, low or high protein intake and high intake of phosphorus, sodium or caffeine. Many of the risk factors are considered to be weak, although when combined they could impact significantly on bone health. Increased intakes of various nutritional factors (potassium, magnesium, zinc, vitamin C), fibre and alkaline-producing fruit and vegetables favour adult bone health. Calcium homeostasis is normally well regulated such that increased calcium loss via the urine leads to increased calcium absorption from the gut. However, the duration of this adaptive process may be greater than that of many of the studies demonstrating that increased salt intake leads to both increased sodium and calcium in the urine. In any case, higher urinary calcium output appears to be seen only in a minority of humans in response to increased salt intake. As numerous factors-genetic, nutritional, hormonal and lifestyle-are involved in the maintenance of calcium homeostasis, it is difficult to devise human studies which adequately take into account all the important factors. Another difficulty is that many past studies have relied on imprecise methods for the measurement of bone resorption. Nor have studies based on the use of the laboratory rat produced clear answers to the problem because the rat, as a species, is uniquely deficient in its ability to handle the relevant minerals. Limited studies to date indicate that increased sodium intake neither exerts a consistent effect on various biomarkers of bone health nor leads to irreversible changes in the bone modelling process in men or in pre- or postmenopausal women. We conclude from the available evidence that increased sodium (or salt) intake is not an important risk factor for osteoporosis and that a reduction of salt intake from 9 to 6g/day in the diet would not be beneficial as an intervention measure in the prevention of osteoporosis. More research is needed to (i) assess the effects (especially long-term) of various nutrients including sodium on bone health, (ii) assess the long-term value of any intervention strategy involving reduced intake of a particular nutrient such as sodium; and (iii) determine whether subpopulations exist particularly in the elderly (e.g. sodium-responsive subjects) in which adaptation to sodium-induced hypercalciuria may be compromised. General prudence dictates that excessively high levels of dietary salt should be eschewed by those persons with raised blood pressure or a limited range of genetic disorders. However, for the generally healthy person there is no sound evidence that the consumption of salt at the present average level of 9g/day constitutes a risk factor for osteoporosis.

Renal effects of low-level environmental cadmium exposure: 5-year follow-up of a subcohort from the Cadmibel study

BACKGROUND

The clinical relevance of renal effects of cadmium in people exposed in the environment remains uncertain. This study examined the evolution of renal effects observed in a population exposed to cadmium in the environment.

METHODS

208 men and 385 women surveyed in 1985-89 (Cadmium in Belgium study [Cadmibel]; baseline) were re-examined on average 5 years later (Public health and environmental exposure to cadmium study [PheeCad]; follow-up). Urinary and blood cadmium and markers of renal tubular dysfunction and glomerular effects were measured. The association between cadmium body burden and renal factors was examined by multivariate logistic and linear regression.

FINDINGS

In men, mean urinary cadmium excretion and blood cadmium concentration measured at follow-up were 7.5 nmol/24 h (SD 1.9) and 6.1 nmol/L (2.2), reductions of 16% and 35% from baseline, respectively. In women, the corresponding values were 7.6 nmol/24 h (1.9) and 7.8 nmol/L (2.1), reductions of 14% and 28% from baseline. No indication of progressive renal damage was found and the overall results suggest that the effects of low environmental exposure to cadmium on the kidney are weak, stable, or reversible.

INTERPRETATION

Subclinical renal effects that have been reported in Belgium in patients with increased cadmium body burden are not associated with progressive renal dysfunction and most likely represent non-adverse manifestations.

Excess dietary protein can adversely affect bone

The average American diet, which is high in protein and low in fruits and vegetables, generates a large amount of acid, mainly as sulfates and phosphates. The kidneys respond to this dietary acid challenge with net acid excretion, as well as ammonium and titratable acid excretion. Concurrently, the skeleton supplies buffer by active resorption of bone. Indeed, calciuria is directly related to net acid excretion. Different food proteins differ greatly in their potential acid load, and therefore in their acidogenic effect. A diet high in acid-ash proteins causes excessive calcium loss because of its acidogenic content. The addition of exogenous buffers, as chemical salts or as fruits and vegetables, to a high protein diet results in a less acid urine, a reduction in net acid excretion, reduced ammonium and titratable acid excretion, and decreased calciuria. Bone resorption may be halted, and bone accretion may actually occur. Alkali buffers, whether chemical salts or dietary fruits and vegetables high in potassium, reverse acid-induced obligatory urinary calcium loss. We conclude that excessive dietary protein from foods with high potential renal acid load adversely affects bone, unless buffered by the consumption of alkali-rich foods or supplements.

The effect of dietary sodium intake on biochemical markers of bone metabolism in young women

To investigate the effect of a low (80 mmol/d) or high (180 mmol/d) Na intake for 14d on biochemical markers of bone turnover in Na-sensitive and Na-non-sensitive healthy young women, twenty-nine subjects were screened for responsiveness of urinary Ca excretion to increasing dietary Na intake (40, 80, 120 and 200 mmol/d for 7 d). In a crossover study, the eight Na-sensitive and eight of the twenty-one Na-non-sensitive subjects were randomly assigned to diets containing either 80 or 180 mmol Na/d for 14d followed by crossover to the alternative diet for a further 14 d. Dietary Ca was restricted to 12.5 mmol/d throughout. During each dietary period, fasting morning first void urine samples (last 3 d) and fasting blood serum samples (morning of twelfth day) were collected. Increasing Na intake from 80 to 180 mmol/d increased urinary Na about twofold in both the Na-sensitive and Na-non-sensitive groups and increased urinary Ca excretion (by 73%) in the Na-sensitive group only. Biochemical markers of bone resorption (urinary pyridinoline and deoxypyridinoline) and bone formation (serum osteocalcin and bone-specific alkaline phosphatase; EC 3.1.3.1) were unaffected by increasing dietary Na in either group. It is concluded that the Na-induced calciuria observed in the Na-sensitive healthy young women did not result in increased bone resorption or turnover and, despite restricted Ca intake, adaptation of dietary Ca absorption may have compensated for the increased urinary Ca loss.

Calcium metabolism and bone calcium content in normal and oophorectomized rats consuming various levels of saline for 12 months

The effect of different intakes of salt for 12 mo on bone calcium content and urinary excretion of calcium and hydroxyproline were examined in sham operated and oophorectomized (OX) rats to determine the long term effects of high sodium intake and its interaction with estrogen deficiency. Sham operated (n = 24) and OX (n = 24) rats were divided into groups of six rats in a 2 x 4 design. One group of sham and one of OX rats were given 0, 2, 6 or 18 g/L sodium chloride to drink. Urine samples were collected at 0, 2, 4, 6, 10 and 12 mo for the measurement of sodium, calcium, creatinine and hydroxyproline. At the end of 12 mo, blood was taken for measurement of calcium, albumin, alkaline phosphatase and creatinine and the left femur was removed and analyzed for calcium and phosphate. Body weights of the OX rats were higher than the sham operated controls. At the start of the experiment (10 d after OX) urinary excretions of calcium and hydroxyproline were significantly higher in OX rats. However, after 4-6 mo, they were significantly lower in OX rats. Calcium excretion and hydroxyproline excretion were increased by high salt intake, and there was a significant correlation between sodium and calcium excretion (r = 0.962). Bone calcium content of OX rats was lower than their corresponding sham-operated controls. Sodium intake also had a significant effect on bone calcium content. Multiple regression analysis showed that OX and sodium intake explained 7.6% and 1.5% of the variation in bone calcium content. We conclude that high sodium intake causes increased loss of calcium and reduces bone calcium content in sham-operated as well as OX rats.

Plasma renin activity is associated with bone mineral density in premenopausal women

Bone mineral density (BMD), plasma renin activity (PRA) and dietary calcium and sodium were evaluated in 47 Caucasian premenopausal women. All subjects were free of any disorder or medications known to affect calcium or bone metabolism. Those subjects with low PRA (< 1.3 ng/ml) had 4.3% lower BMD at the distal radius (p = 0.03). Other skeletal sites appeared to have lower BMD in subjects with low PRA but these differences were not statistically significant. There was a tendency for the low PRA group to have a lower dietary intake of calcium (p = 0.06) as compared with the normal PRA group (> or = 1.3 and < 4.0 ng/ml). Positive correlations were found between calcium intake and PRA (r = 0.26, p = 0.09); and between calcium/sodium intake and distal radial BMD (r = 0.31, p = 0.04), mid-radial BMD (r = 0.30, p = 0.04), total hip BMD (r = 0.23, p = 0.12) and total body BMD (r = 0.27, p = 0.07). This study provides preliminary evidence that a sodium intake > 3400 mg/day, as evidenced by the suppression of PRA, may affect bone mass and the effect may be modified by the level of calcium intake. Additional research is needed to replicate our findings with a larger sample size.

Calcium metabolism, osteoporosis and essential fatty acids: a review

Essential fatty acid (EFA)-deficient animals develop severe osteoporosis coupled with increased renal and arterial calcification. This picture is similar to that seen in osteoporosis in the elderly, where the loss of bone calcium is associated with ectopic calcification of other tissues, particularly the arteries and the kidneys. Recent mortality studies indicate that the ectopic calcification may be considerably more dangerous than the osteoporosis itself, since the great majority of excess deaths in women with osteoporosis are vascular and unrelated to fractures or other bone abnormalities. EFAs have now been shown to increase calcium absorption from the gut, in part by enhancing the effects of vitamin D, to reduce urinary excretion of calcium, to increase calcium deposition in bone and improve bone strength and to enhance the synthesis of bone collagen. These desirable actions are associated with reduced ectopic calcification. The interaction between EFA and calcium metabolism deserves further investigation since it may offer novel approaches to osteoporosis and also to the ectopic calcification associated with osteoporosis which seems to be responsible for so many deaths.

Medical nutrition therapy for patients with osteoporosis

Osteoporosis is a disease of bone fragility that afflicts more than 25 million Americans and costs the economy of the United States approximately $13.8 billion per year. In addition to direct economic costs, osteoporosis frequently costs patients their independence and a decrease in quality of life. Patients with osteoporosis, particularly those with hip fractures, are often older, malnourished persons in need of nutrition assessment and intervention. Such intervention in persons with hip fractures has been shown to be effective in reducing medical costs by decreasing hospital stays and morbidity. We review here a working practice of care at our osteoporosis research center for the medical nutrition therapy of patients with osteoporosis. Medical nutrition therapy includes an evaluation of the patient's health history, social status, and nutrient, intake. On the basis of the assessment, a nutrition care plan can be developed and implemented with the goals of improving clinical outcomes and the quality of life for patients and saving health care dollars.