Low dietary calcium reduces 25-hydroxycholecalciferol in plasma of rats

We investigated whether dietary factors that are known to increase 1,25-(OH)2-cholecalciferol production can deplete plasma 25-OH-cholecalciferol. Plasma concentration of 25-OH-cholecalciferol, its metabolism in vivo and activities of renal mitochondrial 25-OH-cholecalciferol 1-hydroxylase (1-OHase) and 25-OH-cholecalciferol 24-hydroxylase (24-OHase) were measured in rats fed various amounts of calcium (Ca) and phosphorus (P). All diets contained 5 micrograms (200 IU) cholecalciferol per 100 g. For rats fed the "normal" diet (0.7% Ca and 1.2% P) the mean plasma 25-OH-cholecalciferol level was 11.0 +/- 0.8 nmol/L, and the mean 1-OHase activity was 30 +/- 5 fmol/(mg X min). All rats fed the low Ca (0.014%) diet had 1-OHase activities above 200 fmol/(mg X min) and undetectable plasma 25-OH-cholecalciferol levels (less than 2.5 nmol/L). The chi-square test interrelating plasma 25-OH-cholecalciferol and dietary Ca showed statistical significance (P less than 0.001). The high activity of 1-OHase that resulted from dietary Ca restriction increased utilization of 25-OH-cholecalciferol to the point of causing depletion of this metabolite in the circulation.     

Influence of dietary phosphorus restriction on calcium and phosphorus metabolism in rats

The effect of dietary phosphorus (P) on calcium (Ca) and phosphorus metabolism was studied in young female rats. P levels in the semipurified diets ranged from 0.1 to 0.4% (w/w). A level of 0.4% P in the diet is recommended for rats. Kidney calcification was observed in rats fed the 0.4%-P diet whereas P restriction prevented this condition. Rats fed the diet containing 0.1% P, showed severe hypercalciuria, hypercalcemia, reduced growth and impaired bone mineralization. These effects did not occur when the diet contained 0.2 or 0.3% of P. This study suggests that in short-term studies P in the diet of female rats can be restricted to 0.2% so as to prevent nephrocalcinosis without affecting their development.     

The effects of dietary levels of inorganic phosphorus, calcium and cholecalciferol on the digestibility of phytate-P by the chick.

Male broiler chicks (1-d-old; Ross one) were given either a control diet containing recommended levels of phosphorus, calcium and cholecalciferol or experimental diets low in P and with variable levels of Ca (normal and low) and cholecalciferol (normal or high). The low-P diet with normal levels of Ca and cholecalciferol induced a hypophosphataemia and a hypercalcaemia which was reflected in reduced tibia length and weight and in reduced Ca, P and magnesium contents of tibia. The phytate digestibility remained normal while the retention of P and Ca fell significantly. The lowering of Ca alone elevated phytate digestibility and restored P and Ca retention. The hypercalcaemia and hypophosphataemia remained and tibia mineralization remained impaired. The raising of cholecalciferol alone dramatically increased phytate digestibility and the retention of Ca and P. While this remedied the hypercalcaemia, the hypophosphataemia persisted as did the diminution of tibia weight. The simultaneous lowering of dietary Ca and elevation of cholecalciferol on low-P diets restored all variables to the levels for the control diet. Circulating levels of 1,25-dihydroxycholecalciferol were significantly elevated by low-P diets, more so with high cholecalciferol intakes. However, Ca did not influence 1,25-dihydroxycholecalciferol levels in plasma.     

Influence of dietary potassium on lysine metabolism in the chick

High levels of dietary cations have been reported to spare the arginine requirement of chicks fed a diet containing excess lysine. The present studies were conducted to determine the nature of this effect, using potassium as the variable cation. The inclusion of 1.8% potassium in a high lysine diet improved growth but did not affect consistently the efficiency of feed utilization, nor did it have a significant effect on arginine metabolism as measured by renal arginase activity, urea excretion or arginine excretion. Lysine catabolism was markedly increased, however. Chicks fed the potassium supplemented diet converted approximately 23% of an oral loading dose of 14C lysine to respiratory 14CO2 over a 6-hour period, in contrast to approximately 9% of the dose in chicks fed the unsupplemented diet containing 0.4% potassium. The activity of hepatic lysine-alpha-ketoglutarate reductase, an initial enzyme in the catabolism of lysine, was increased in response to potassium or arginine supplementation. It is proposed that high levels of potassium or other cations may improve the growth of chicks fed diets containing excess lysine by increasing lysine catabolism. The effect on growth may be mediated primarily by increasing food intake and to a lesser extent by alleviation of the other metabolic manifestation of the lysine-arginine antagonism.     

The effects of dietary calcium and phosphorus on the retention and excretion of lead in rats.

1. Rats were given diets containing different amounts of calcium, phosphorus and lead. 2. Pb retention was greatly increased when the diets contained less Ca or P than the minimum estimated requirement of the rat. 3. The release of Pb already incorporated into the skeleton was inhibited by diets low in Ca but was not affected by diets low in P. 4. The retention of Pb given intraperitoneally was not affected by dietary Ca or P. 5. It can be concluded that dietary Ca and P influence the absorption of Pb by the gut and dietary Ca influences the metabolism of Pb in the bone. 6. There were changes in the distribution of Pb among the tissues due to changes of dietary Ca. 7. At low body concentrations, Pb probably affected skeletal growth.     

慢性肾脏病患者饮食磷摄入现状及与钙磷代谢相关性研究

目的 探讨慢性肾脏病患者饮食磷摄入情况,并分析饮食中磷摄入量对血营养指标及钙磷代谢相关指标的影响。方法 以2018年12月至2019年11月成都市某医院诊治的慢性肾脏病患者为研究对象,进行基本资料收集、3 d 24 h膳食调查、营养状态评估及血生化指标检测,采用描述流行病学分析方法对慢性肾脏病患者饮食磷摄入量进行分析。结果 共对151例慢性肾脏病患者进行研究,患者年龄25~75岁,以60~75岁为主,占64.9%,男女性别比为1.25∶ 1,疾病分期以3期为主,占49.0%,原发病以肾小球肾炎为主,占70.9%,主观营养评估（SGA）法评定结果以B级（可疑营养不良）为主,占86.1%。饮食磷摄入量以中等水平（600~800 mg/d）为主,占58.6%,其次是高水平（>800 mg/d）,占23.6%,摄入量低水平（<600 mg/d）的占17.8%。不同饮食磷摄入量的慢性肾脏病患者白蛋白、前白蛋白、血磷、血磷钙乘积指标差异均有统计学意义（均P<0.01）,转铁蛋白、血钙水平在不同饮食磷摄入量慢性肾脏病患者中的差异均无统计学意义（均P>0.05）。血磷及血钙磷乘积与饮食磷摄入量呈正相关（r_s=0.736、0.809,均P<0.05）。结论 饮食磷摄入量对慢性肾脏病患者的营养状况和磷代谢有一定影响,慢性肾脏病患者应注意按营养师的指导注意挑选钾含量较低的食物,在保证机体生理需求前提下,有效控制磷的摄入量,预防高磷血症的发生。     

Dietary metformin effects on in vitro and in vivo metabolism in the chicken

Chickens were fed diets containing 0, 0.25, 0.5, and 1 and 0, 2.5, 5, and 10 g metformin (MET)/kg diet in 2 separate experiments to determine whether MET (1,1 dimethylbiguanidine hydrochloride) regulated plasma glucose and, possibly, feed intake in broiler chickens. Feed intakes in the first experiment were equal, but, in the second experiment, MET at 5 and 10 g/kg reduced feed intake. The first series of diets had no effect on plasma glucose and lactate. The second series of dietary treatments did not affect plasma glucose but did increase plasma lactate, uric acid, and triglycerides linearly. In the second experiment, there were significant decreases in lipogenesis that accompanied increasing doses of MET. The increase in plasma lactic acid suggests that MET stimulates pyruvate kinase in the chicken, as it does in mammals. The lack of effect on plasma glucose also suggests that regulation occurs downstream of pyruvate in the chicken. These findings may explain MET's ability to reduce hepatic triglyceride synthesis and suppress appetite.     

The effect of variation in dietary protein or mineral supply on calcium and phosphorus metabolism in lactating ewes

Two experiments are described in which changes in both nitrogen and mineral balance were monitored in ewes during lactation. In Expt 1, two groups (n 6) of ewes were fed on diets that were either high (15 g crude protein (N X 6.25; CP)/MJ metabolizable energy (ME)) or low (10 g CP/MJ ME) in protein content, and concurrent N and mineral balance studies were made at intervals during lactation with 45Ca and 32P being used to monitor faecal endogenous calcium and phosphorus losses. Ewes fed on the high-protein diet maintained a positive N balance during early lactation, whereas those fed on the low-protein diet were in negative N balance. Both groups, however, showed the same degree of negative Ca and P balance, with the amounts lost being directly related to milk yield. This indicates that loss of mineral from the skeleton at this time is not secondary to a loss of bone matrix due to a shortfall in dietary protein supply. In Expt 2, two groups of ewes (n 4) were fed on diets in late pregnancy that were either just adequate or generous in Ca and P supply relative to requirement (TCORN, 1990). After parturition both groups were fed on a diet which was formulated to meet their estimated Ca and P requirements for lactation. As in the previous experiment both groups were in negative Ca and P balance in early lactation and variation in dietary Ca and P supply during pregnancy had no effect on the extent of this loss. Alternative explanations for the cause of this loss of mineral from the skeleton are discussed.     

Mono- and polyphosphates have similar effects on calcium and phosphorus metabolism in healthy young women

Purpose

Phosphate (Pi) salts, often mono- (MP) or polyphosphates (PP), are commonly used as additives in the food industry. Previous studies have shown that the effects of MP and PP on calcium (Ca) and phosphorus (P) metabolism may differ. The aim of this study was to determine whether the effects of MP and PP salts differ on markers of Ca and P metabolism in young women.

Methods

Fourteen healthy women 19–31 years of age were randomized into three controlled 24-h study sessions, each subject serving as her own control. During each session, the subjects received three doses of MP, PP or a placebo with meals in randomized order. Both Pi salts provided 1,500 mg P/d, and the diet during each session was identical. Markers of Ca and P metabolism were followed six times over 24 h.

Results

During both MP and PP sessions, we found an increase in serum phosphate (S-Pi, p = 0.0001), urinary phosphate (U-Pi, p = 0.0001) and serum parathyroid hormone (S-PTH, p = 0.048 MP, p = 0.012 PP) relative to the control session. PP decreased U-Ca more than did MP (p = 0.014).

Conclusions

The results suggest that PP binds Ca in the intestine more than does MP. Based on the S-Pi, U-Pi and S-PTH results, both Pi salts are absorbed with equal efficiency. In the long run, increased S-PTH, caused by either an MP or PP salt, could have negative effects on bone metabolism.     

Relative toxicity and metabolic effects of cholecalciferol and 25-hydroxycholecalciferol in chicks.

The relative toxicity and metabolic effectiveness of cholecalciferol (CC) and 25-hydroxycholecalciferol (25-HCC) in chicks were evaluated by feeding six graded levels of each and observing gross and microscopic pathology as well as several metabolic parameters of calcium metabolism. Renal tubular calcification was observed when CC was fed at the rate of 10.0 mg/kg of diet and when 25-HCC was fed at the rate of 0.1 mg/kg diet. Thus, 100-fold increase in toxicity results when the hydroxylated form of CC is fed. Both microscopic renal lesions and increased renal calcium and inorganic phosphate concentrations occurred in chicks with normal serum calcium concentrations.     

Effect of calcium and phosphorus on zinc metabolism in man

Calcium and phosphorus have been shown to inhibit the availability of zinc for absorption in animal studies, but limited information is available on this subject in man. In the present study, the effect of both calcium and phosphorus on zinc metabolism was investigated in adult men by determining metabolic balances of zinc during three intake levels of calcium of 200, 800, and 2000 mg/day, and during two intake levels of phosphorus of 800 and 2000 mg/day. The analyzed dietary zinc intake was normal and was kept constant throughout all study phases. Increasing the calcium intake from 200 mg to two higher intake levels up to 2000 mg/day did not significantly change the urinary or fecal zinc excretions or the zinc balance. Also, increasing the phosphorus intake from 800 to a high intake of 2000 mg/day did not have any effect. The simultaneous use of the high calcium and high phosphorus intake also had no effect on zinc excretions and on the zinc balance.     

The acute effects of different sources of dietary calcium on postprandial energy metabolism

Dairy Ca intake has been shown to be superior to elemental Ca in increasing the loss of body fat during energy restriction. We questioned whether the mechanisms involved an increase in postprandial energy expenditure, fat oxidation and/or a greater lipolysis. The acute effects of different sources of Ca were examined in eight subjects, aged 47-66 years and BMI 27.6-36.1 kg/m2, in a three-way cross-over study. Subjects were randomly provided breakfast meals either low in dairy Ca and vitamin D (LD; control), high in non-dairy Ca (calcium citrate) but low in vitamin D (HC) or high in dairy Ca and vitamin D (HD). Diet-induced thermogenesis, fat oxidation rates (FOR), carbohydrate oxidation rates (COR), insulin, glucose, NEFA and glycerol were measured hourly over a 6 h postprandial period. Postprandial data were calculated as a change (Delta) from the fasting value. Results showed that DeltaNEFA was significantly different between meals (LD -1.50 (sem 0.26), HC -1.22 (sem 0.32), HD -0.94 (sem 0.27) mmol/l x 6 h; P = 0.035), with a lesser suppression following both high-Ca meals. DeltaFOR was significantly higher following the two high-Ca meals (LD -6.5 (sem 2.2), HC 2.93 (sem 2.34), HD 3.3 (sem 2.5) g x 6 h; P = 0.005), while reciprocally DeltaCOR was significantly lower. DeltaGlycerol was less suppressed following the high-Ca meals but statistical significance was not achieved. No differences in diet-induced thermogenesis, insulin or glucose were observed. Regardless of source, Ca intake acutely stimulated postprandial fat oxidation; and there was a lesser suppression of NEFA following these meals.