Effects of Vitamin K2 Administration on Calcium Balance and Bone Mass in Young Rats Fed Normal or Low Calcium Diet

The influence of vegetarian and vegan diets on the state of bone mineral density in humans

There are so many literatures about vegetarians being less prone to chronic, noninfectious diseases, which are, however, the main cause of the decline in quality of life and mortality in developed countries.However, according to various scientific sources, vegetarian and especially vegan diets often contain less saturated fats, protein, calcium, vitamins D and B12, or long-chain ω-3 PUFAs. One of the most common pathology associated with a predominantly plant diet is osteopenia and osteoporosis. An analysis of 13 studies has shown that vegetarians and vegans are at a higher risk of reducing of bone mineral density, thereby increasing the incidence of fractures.At the same time, plant-based diets are usually richer in many other micronutrients important for bone health: vitamins C and K, carotenoids, potassium, magnesium, manganese, copper, or silicon. Moreover, with the deepening of our knowledge about the role of nutrients in the body and the features of the nutritional status of the population, the quality of vegetarian and vegan diets also increases. They are less and less prone to micronutrient deficiencies. Recent studies show that BMD, as well as the risk of osteoporotic fractures, at least in vegetarians, equaled these indicators in omnivores.

Gastrointestinal calcium absorption in sheep is mostly insensitive to an alimentary induced challenge of calcium homeostasis

For ruminants, marked differences to monogastric species have been described concerning the localisation and vitamin D sensitivity of gastrointestinal calcium absorption, particularly with respect to the forestomach compartment. Therefore, we investigated gastrointestinal calcium transport of sheep as influenced by a dietary calcium restriction and/or a supraphysiological dosage of exogenous calcitriol. Using the Ussing chamber technique, we determined calcium and mannitol flux rates to differentiate between para- and transcellular calcium transport in rumen, duodenum, jejunum and colon. Expression of epithelial calcium channels, calbindin-D(9K), and basolateral extrusion mechanisms was determined by quantitative RT-PCR and Western blot analysis. Active calcium transport could be demonstrated in jejunum and rumen. A significant stimulation of jejunal calcium absorption was only observed in animals treated with calcitriol. The alimentary calcium restriction alone did not result in significant effects indicating a less effective intestinal adaptation to alimentary calcium restriction than observed in monogastric animals. The observed ruminal calcium transport was not affected at all, neither by the diet nor the calcitriol treatment. Furthermore, no significant expression of epithelial calcium channels or calbindin-D(9K) could be detected in the rumen; therefore it is concluded that calcium transport in the forestomachs is probably mediated by a different, so far unknown mechanism.

Effects of 1,25-dihydroxyvitamin D3 on calcium and phosphorus homeostasis in sheep fed diets either adequate or restricted in calcium content

It was the aim of the present study to collect basic data on calcium (Ca) and phosphorus (P) homoeostasis in sheep. Two series of experiments were carried out to investigate the effects of 1,25-dihydroxyvitammin D(3) (calcitriol) in supraphysiological dosage in combination with varying alimentary Ca supply. In the first series, blood samples were collected over 72 h to determine the concentrations of total Ca (Ca), ionized Ca (Ca(2+)), inorganic phosphate (P(i)), and the bone resorption marker CrossLaps (CL). In the second series, measurements were carried out over 12h. In addition, urine samples were collected to calculate the fractional excretions (FE) of Ca and P(i). Changes in plasma macromineral concentrations (P<0.01) as well as in CL (P<0.001) and endogenous calcitriol (P<0.05) were observed in the alimentary Ca-restricted animals, indicating that the reduction of daily Ca intake challenged the animals' macromineral homeostatic mechanisms. However, the Ca-restricted diet had an effect on neither FE of Ca nor on FE of P(i). The treatment resulted in peak serum calcitriol concentrations between 1,900 and 2,500 pg/mL, and supraphysiological concentrations were maintained for the next 48 h. Irrespective of dietary Ca, calcitriol had hypercalcemic and hyperphosphatemic effects. An increase in CL was revealed only in the Ca-restricted, calcitriol-treated sheep (P<0.01), reflecting a remarkable enhancement of Ca mobilization from the bone by calcitriol exclusively in this group. From these data, it can be concluded that the sheep can be a suitable animal model for studying catabolic effects of Ca deficiency and calcitriol on bone metabolism.