Enhanced dietary Ca intake linearly increases intestinal Ca absorption in pigs, but not in broilers, suggesting potential differences in whole body Ca homeostasis. To determine the role of kidney in Ca homeostasis in these species, we varied in growing pigs in experiment (Exp) 1, the dietary Ca content 2·0 v. 9·6 g/kg and phytase 0 v. 500 FTU/kg, in broilers, in Exp 2 the dietary Ca/retainable P from 1·3 to 2·8 and phytase 0 v. 1000 FTU/kg, and in Exp 3 dietary Ca/P from 0·50 to 1·75. Increasing dietary Ca reduced renal mRNA expression of Ca-related transporters (TRPV5, TRPV6, CaBP-D28k and NCX1) and tight junctions (CLDN-12 and −16) in pigs, indicating Ca reabsorption was reduced to maintain Ca homeostasis. In broilers (Exp 2), high dietary Ca increased renal TRPV6, CaBP-D28k and CLDN-2 mRNA, indicating an increased capacity for Ca reabsorption. Moreover, the effect of dietary Ca was enhanced by inclusion of dietary phytase in pigs but reduced in broilers. Furthermore, increasing dietary Ca upregulated inorganic phosphate transporter 1 (PiT-1), while phytase downregulated xenotropic and polytropic retrovirus receptor 1 (XPR1) mRNA expression in pigs; in broilers, dietary Ca downregulated renal mRNA expression of Na-dependent phosphate transporter IIa (NaPi-IIa), PiT-1, PiT-2 and XPR1, while phytase downregulated NaPi-IIa but upregulated PiT-2 and XPR1 mRNA expression. In Exp 3, Ca/P effect on transporter mRNA expression was largely consistent with Exp 2. In conclusion of this study, together with previously measured data about Ca and P homeostasis, in pigs the kidneys play a more regulatory role in Ca homeostasis than in broilers where the intestine is more important for regulation.

Ruminants can recycle nitrogen (N) and phosphorus (P), which are essential for vital body processes. Reduced N- and P-intake in ruminants is desirable for economic and ecologic reasons. Simultaneous modulation of mineral homoeostasis and bone metabolism occurs in young goats. This study aimed to investigate potential effects of dietary N- and/or P-restriction on molecular changes in bone metabolism. The twenty-eight young male goats were fed a control diet, an N-reduced diet, a P-reduced diet or a combined N- and P-reduced diet for 6–8 weeks. The N-restricted goats had lower plasma Ca concentration and higher plasma osteocalcin (OC) and CrossLaps concentrations. The P-restricted goats had reduced plasma inorganic phosphate (Pi) concentrations and increased plasma Ca concentrations. Due to the initiation of a signalling pathway that inhibits the fibroblast growth factor 23 (FGF23) expression, this was lower with P-restriction. Consequently, lower Pi concentrations were the main factor influencing the reduction in FGF23. The changes in mineral homoeostasis associated with P-restriction led to a reduction in OC, bone mineral content and mineral density. Simultaneously, bone resorption potentially increased with P-restriction as indicated by an increased receptor activator of NF-κB ligand/osteoprotegerin (OPG) ratio and an increase in OPG mRNA expression. Additionally, the increased mRNA expression of the calcitonin receptor during P-restriction points to a higher number of osteoclasts. This study demonstrates an impairment of bone remodelling processes in young goats by N- or P-restriction. With P-restriction, bone mineralisation rate was potentially reduced and bone quality impaired, while with N-restriction, bone remodelling increased.

Vitamin D deficiency has previously been linked to higher rates of exacerbation and reduced lung function in asthmatics. Previous randomised controlled trials investigating the effect of vitamin D supplementation have mainly focused on children with asthma. Trials involving adults have typically used bolus dosing regimens, and the main outcomes have been patient-focused without investigating underlying inflammation. The present study aimed to conduct a 12-week placebo-controlled randomised controlled trials administering a daily 125 µg vitamin D3 supplement to adults with mild to moderate asthma. A total of 32 participants were randomised to receive either the 125 μg vitamin D3 supplement or an identical matching placebo. The primary outcome of the study was lung function measured by the ratio of FEV1:FVC (effect size 2·5) with secondary outcomes including asthma symptoms and inflammatory biomarkers. There was a small but statistically significant higher increase in the mean (±sd) ratio of FEV1:FVC from baseline to post-intervention in the vitamin D group (+0·05 ± 0·06) compared with the placebo group (+0·006 ± 0·04, P = 0·04). There was no effect of the intervention on asthma control test scores, or the inflammatory biomarkers measured. There was a moderate, significant association between baseline plasma 25(OH)D concentration and baseline plasma IL-10 (r = 0·527, P = 0·005) and TNF-α (r = −0·498. P = 0·008) concentrations. A daily vitamin D3 supplement led to slightly improved lung function in adult asthmatics and may be a useful adjunct to existing asthma control strategies, particularly for individuals with suboptimal vitamin D status.

Vitamin D is a vital indicator of musculoskeletal health, as it plays an important role through the regulation of bone and mineral metabolism. This meta-analysis was performed to investigate the effects of vitamin D supplementation/fortification on bone turnover markers in women. All human randomised clinical trials reported changes in bone resorption markers (serum C-terminal telopeptide of type-I collagen (sCTX) and urinary type I collagen cross-linked N-telopeptide (uNTX)) or bone formation factors (osteocalcin (OC), bone alkaline phosphatase (BALP) and procollagen type-1 intact N-terminal propeptide (P1NP)) following vitamin D administration in women (aged ≥ 18 years) were considered. Mean differences (MD) and their respective 95 % CI were calculated based on fixed or random effects models according to the heterogeneity status. Subgroup analyses, meta-regression models, sensitivity analysis, risk of bias, publication bias and the quality of the included studies were also evaluated. We found that vitamin D supplementation had considerable effect on sCTX (MD: −0·038, n 22) and OC (MD: −0·610, n 24) with high heterogeneity and uNTX (MD: −8·188, n 6) without heterogeneity. Our results showed that age, sample size, dose, duration, baseline vitamin D level, study region and quality of studies might be sources of heterogeneity in this meta-analysis. Subgroup analysis also revealed significant reductions in P1NP level in dose less than 600 μg/d and larger study sample size (>100 participants). Moreover, no significant change was found in BALP level. Vitamin D supplementation/fortification significantly reduced bone resorption markers in women. However, results were inconsistent for bone formation markers.

Calcium and vitamin D have well-established roles in maintaining calcium balance and bone health. Decades of research in human subjects and animals have revealed that calcium and vitamin D also have effects on many other organs including male reproductive organs. The presence of calcium-sensing receptor, vitamin D receptor, vitamin D activating and inactivating enzymes and calcium channels in the testes, male reproductive tract and human spermatozoa suggests that vitamin D and calcium may modify male reproductive function. Functional animal models have shown that vitamin D deficiency in male rodents leads to a decrease in successful mating and fewer pregnancies, often caused by impaired sperm motility and poor sperm morphology. Human studies have to a lesser extent validated these findings; however, newer studies suggest a positive effect of vitamin D supplementation on semen quality in cases with vitamin D deficiency, which highlights the need for initiatives to prevent vitamin D deficiency. Calcium channels in male reproductive organs and spermatozoa contribute to the regulation of sperm motility and capacitation, both essential for successful fertilisation, which supports a need to avoid calcium deficiency. Studies have demonstrated that vitamin D, as a regulator of calcium homoeostasis, influences calcium influx in the testis and spermatozoa. Emerging evidence suggests a potential link between vitamin D deficiency and male infertility, although further investigation is needed to establish a definitive causal relationship. Understanding the interplay between vitamin D, calcium and male reproductive health may open new avenues for improving fertility outcomes in men.

Sufficient vitamin D status is crucial for successful pregnancy and fetal development. The assessment of 25-hydroxyvitamin D (25(OH)D) concentrations is commonly used to evaluate vitamin D status. Our objective was to examine the interrelated biodynamics of maternal and neonatal total, free and bioavailable 25(OH)D in maternal–neonatal dyads at birth and their associations with homeostasis and neonatal birth anthropometry. We analysed a cohort of seventy full-term mother–child pairs. We found positive associations between all neonatal measures of vitamin D status. Maternal forms exhibited a similar pattern of association, except for the bioavailable maternal form. In multivariate analysis, both total and free maternal 25(OH)D concentrations were correlated with all neonatal forms (neonatal total 25(OH)D: 1·29 (95 % CI, 1·12, 1·46) for maternal total 25(OH)D, 10·89 (8·16, 13·63) for maternal free 25(OH)D), (neonatal free 25(OH)D: 0·15 for maternal total 25(OH)D, 1·28 (95 % CI, 0·89, 1·68) for maternal free 25(OH)D) and (0·13 (95 % CI, 0·10, 0·16), 1·06 (95 % CI, 0·68, 1·43) for maternal free 25(OH)D), respectively, with the exclusion of the bioavailable maternal form. We observed no significant interactions within or between groups regarding maternal and neonatal vitamin D parameters and maternal calcium and parathyroid hormone concentrations, and neonatal birth anthropometry. Our study indicates that bioavailable maternal and neonatal 25(OH)D have no significant effects on vitamin D equilibrium, Ca homeostasis and neonatal anthropometry at birth. However, we observed an interaction between maternal and neonatal total and free 25(OH)D concentrations at the maternal–neonatal interface, with no associations observed with other calciotropic or anthropometric outcomes.

Obesity is associated with low vitamin D status, and the optimal supplement and dosage of cholecalciferol (vitamin D3) or calcidiol (25OHD) for individuals with obesity have been debated. We aimed to determine the effect of high-dose vitamin D3 supplementation on achieving adequate vitamin D levels among infertile men with normal weight v. obesity. Here, we present secondary end points from a single-centre, double-blinded, randomised clinical trial, comprising 307 infertile men randomised to active or placebo treatment for 150 days. Men in the active group initially received an oral bolus of 300 000 mg of vitamin D3, followed by daily supplementation with 1400 mg of vitamin D3 and 500 mg of calcium. Baseline BMI was listed as a predefined subgroup. At baseline, serum 25OHD was significantly higher in men with normal weight (BMI < 25 kg/m2) compared with men with overweight (BMI 25–30 kg/m2) and obesity (BMI > 30 kg/m2) (48 nmol/l v. 45 nmol/l and 39 nmol/l, respectively; P = 0·024). After the intervention, men with normal weight, overweight and obesity treated with vitamin D3 had a significantly higher serum 25OHD compared with corresponding placebo-treated men (BMI < 25 kg/m2: 92 nmol/l v. 53 nmol/l, BMI = 25–30 kg/m2: 87 nmol/l v. 49 nmol/l and BMI > 30 kg/m2: 85 nmol/l v. 48 nmol/l; P < 0·001 for all, respectively). In conclusion, we show that high-dose vitamin D3 supplementation to infertile men with obesity and low vitamin D status is sufficient to achieve adequate serum 25OHD levels.

This study investigated sex differences in Fe status, and associations between Fe status and endurance and musculoskeletal outcomes, in military training. In total, 2277 British Army trainees (581 women) participated. Fe markers and endurance performance (2·4 km run) were measured at the start (week 1) and end (week 13) of training. Whole-body areal body mineral density (aBMD) and markers of bone metabolism were measured at week 1. Injuries during training were recorded. Training decreased Hb in men and women (mean change (–0·1 (95 % CI –0·2, –0·0) and –0·7 (95 % CI –0·9, –0·6) g/dl, both P < 0·001) but more so in women (P < 0·001). Ferritin decreased in men and women (–27 (95 % CI –28, –23) and –5 (95 % CI –8, –1) µg/l, both P ≤ 0·001) but more so in men (P < 0·001). Soluble transferrin receptor increased in men and women (2·9 (95 % CI 2·3, 3·6) and 3·8 (95 % CI 2·7, 4·9) nmol/l, both P < 0·001), with no difference between sexes (P = 0·872). Erythrocyte distribution width increased in men (0·3 (95 % CI 0·2, 0·4)%, P < 0·001) but not in women (0·1 (95 % CI –0·1, 0·2)%, P = 0·956). Mean corpuscular volume decreased in men (–1·5 (95 % CI –1·8, –1·1) fL, P < 0·001) but not in women (0·4 (95 % CI –0·4, 1·3) fL, P = 0·087). Lower ferritin was associated with slower 2·4 km run time (P = 0·018), sustaining a lower limb overuse injury (P = 0·048), lower aBMD (P = 0·021) and higher beta C-telopeptide cross-links of type 1 collagen and procollagen type 1 N-terminal propeptide (both P < 0·001) controlling for sex. Improving Fe stores before training may protect Hb in women and improve endurance and protect against injury.

Dogs are considered omnivores based on their evolution consuming diets including animal tissue. Few feeding trials evaluating the nutritional suitability of exclusively plant-based (vegan) diets in dogs have been published, and the efficacy of vitamin D2 in maintaining canine serum vitamin D levels has not been clearly determined. A blinded dietary trial included sixty-one healthy desexed adult dogs: thirty-one fed an experimental extruded vegan diet (PLANT) and thirty fed a commercial extruded meat-based diet (MEAT) for 3 months. Dogs were screened via veterinary examination and routine laboratory analyses prior to enrolment, at baseline and exit timepoints. Body composition was measured by dual-energy X-ray absorptiometry and blood was collected for vitamin D profiling. All dogs maintained health parameters, body weight and composition throughout the study. Dogs maintained on PLANT demonstrated a significant reduction in platelet count, creatinine, blood urea nitrogen and cholesterol, though values remained within normal reference ranges. Dogs fed PLANT also demonstrated a shift from vitamin D3 to vitamin D2 metabolites, though total vitamin D analogue levels were unchanged, with the exception of 24,25-dihydroxyvitamin D. Bone mineral content and density did not differ from baseline values. Health status was maintained in dogs fed PLANT and vitamin D2 appeared efficacious in maintaining serum total vitamin D concentrations and bone mineralisation. Findings support the hypothesis that PLANT was comparable to MEAT for maintenance of healthy adult dogs for at least 3 months and identified areas where further research is warranted to elucidate the potential risks and benefits of plant-based (vegan) diets.

The transition towards more plant-based diets may pose risks for bone health such as low vitamin D and Ca intakes. Findings for the contribution of animal and plant proteins and their amino acids (AA) to bone health are contradictory. This 6-week clinical trial aimed to investigate whether partial replacement of red and processed meat (RPM) with non-soya legumes affects AA intakes and bone turnover and mineral metabolism in 102 healthy 20–65-year-old men. Participants were randomly assigned to diet groups controlled for RPM and legume intake (designed total protein intake (TPI) 18 E%): the meat group consumed 760 g RPM per week (25 % TPI) and the legume group consumed non-soya legume-based products (20 % TPI) and 200 g RPM per week, the upper limit of the Planetary Health Diet (5 % TPI). No differences in bone (bone-specific alkaline phosphatase; tartrate-resistant acid phosphatase 5b) or mineral metabolism (25-hydroxyvitamin D; parathyroid hormone; fibroblast growth factor 23; phosphate and Ca) markers or Ca and vitamin D intakes were observed between the groups (P > 0·05). Methionine and histidine intakes were higher in the meat group (P ≤ 0·042), whereas the legume group had higher intakes of arginine, asparagine and phenylalanine (P ≤ 0·013). Mean essential AA intakes in both groups met the requirements. Increasing the proportion of non-soya legumes by reducing the amount of RPM in the diet for 6 weeks did not compromise bone turnover and provided on average adequate amounts of AA in healthy men, indicating that this ecologically sustainable dietary change is safe and relatively easy to implement.

Expression levels of genes (RT-qPCR) related to Ca and P homeostasis (transporters and claudins (CLDN)) were determined in porcine jejunal and colonic mucosa. Forty growing pigs (BW 30·4 (sem 1·3) kg) received a low and high Ca content (2·0 and 9·6 g/kg, respectively) diet with or without microbial phytase (500 FTU/kg) for 21 d. Dietary Ca intake enhanced serum Ca and alkaline phosphatase concentration and reduced P, 1,25(OH)2D3, and parathyroid hormone concentration. Jejunal transient receptor potential vanilloid 5 (TRPV5) mRNA expression was decreased (32%) with phytase inclusion only, while colonic TRPV5 mRNA was reduced by dietary Ca (34%) and phytase (44%). Both jejunal and colonic TRPV6 mRNA expression was reduced (30%) with microbial phytase. Calbindin-D9k mRNA expression was lower in colonic but not jejunal mucosa with high dietary Ca (59%) and microbial phytase (37%). None of the mRNAs encoding the Na–P cotransporters (NaPi-IIc, PiT-1, PiT-2) were affected. Jejunal, but not colonic expression of the phosphate transporter XPR1, was slightly downregulated with dietary Ca. Dietary Ca downregulated colonic CLDN-4 (20%) and CLDN-10 (40%) expression while CLDN-7 was reduced by phytase inclusion in pigs fed low dietary Ca. Expression of colonic CLDN-12 tended to be increased by phytase. In jejunal mucosa, dietary Ca increased CLDN-2 expression (48%) and decreased CLDN-10 (49%) expression, while phytase slightly upregulated CLDN-12 expression. In conclusion, compared with a Ca-deficient phytase-free diet, high dietary Ca and phytase intake in pigs downregulate jejunal and colonic genes related to transcellular Ca absorption and upregulate Ca pore-forming claudins.

The aim of the study was to compare the efficacy of daily v. weekly oral vitamin D3 therapy in radiological healing of nutritional rickets. Children 6 months to 12 years (n 132) diagnosed with nutritional rickets were randomised into three groups (n 44): group A – 2000 IU daily vitamin D3 for 12 weeks, B – 60 000 IU weekly for 3 weeks, C – 60 000 IU weekly for 6 weeks. Serum calcium, phosphorus, 25-hydroxyvitamin D (25(OH)D), parathyroid hormone and X-ray score were estimated at baseline and 12 weeks (endline). The proportion of children who achieved complete radiological healing at endline was compared between three groups by χ2 and delta change in laboratory parameters by ANOVA (parametric data) or Kruskal Wallis test (non-parametric data), respectively. Baseline 25(OH)D ≤ 20 ng/ml was seen in 119 (90·2 %), hyperparathyroidism in 90 (68·8 %) and hypocalcaemia in 96 (72·7 %). A total of 120/132 children completed the study. Complete radiological healing seen in 30 (75 %) in group A, 23 (60·5 %) in group B and 26 (61·9 %) in group C; P = 0·15, with comparable endline X-ray scores; P = 0·31. The median (interquartile range (IQR)) delta X-ray score (baseline–endline) was 7 (4,9), 5 (2·25, 6) and 6 (4,7) in groups A, B and C, respectively; P = 0·019. Median (IQR) 25(OH)D endline levels in groups A, B and C were 50·0 (26·5, 66·5), 42·1 (28·4, 54·4) and 53·5 (33·7, 71·2) ng/ml, respectively; P = 0·045. Radiological scores were comparable at endline among daily and weekly vitamin D groups with greater change from baseline in daily supplemented group.

The ubiquity of vitamin D metabolising enzymes and vitamin D receptors in mammalian organisms suggests that vitamin D has pleiotropic effects. There are quite a few studies indicating the anticancer, cardioprotective and antidiabetic effects of vitamin D; however, the best-documented actions of vitamin D are the regulation of Ca–phosphate balance and its effect on immune function.

Vitamin D levels in organisms are modulated by many environmental and non-environmental factors. One potential factor that may influence vitamin D levels and effects is the sex of the individuals studied. This review focuses on the scientific evidence indicating different synthesis and metabolism of vitamin D in females and males, mainly from PubMed database sources. The article verifies the sex differences in vitamin D levels reported around the world. Moreover, the different effects of vitamin D on the musculoskeletal, cardiovascular, nervous and immune systems, as well as cancer in males and females, were discussed.

Most studies addressing sex differences in vitamin D levels and effects are observational studies with conflicting results. Therefore, carefully designed clinical trials and experiments on animal models should be carried out to determine the role of non-environmental factors that may differentiate vitamin D levels in females and males.

Maintaining Mg status may be important for military recruits, a population that experiences high rates of stress fracture during initial military training (IMT). The objectives of this secondary analysis were to (1) compare dietary Mg intake and serum Mg in female and male recruits pre- and post-IMT, (2) determine whether serum Mg was related to parameters of bone health pre-IMT, and (3) whether Ca and vitamin D supplementation (Ca/vitamin D) during IMT modified serum Mg. Females (n 62) and males (n 51) consumed 2000 mg of Ca and 25 μg of vitamin D/d or placebo during IMT (12 weeks). Dietary Mg intakes were estimated using FFQ, serum Mg was assessed and peripheral quantitative computed tomography was performed on the tibia. Dietary Mg intakes for females and males pre-IMT were below the estimated average requirement and did not change with training. Serum Mg increased during IMT in females (0·06 ± 0·08 mmol/l) compared with males (–0·02 ± 0·10 mmol/l; P < 0·001) and in those consuming Ca/vitamin D (0·05 ± 0·09 mmol/l) compared with placebo (0·001 ± 0·11 mmol/l; P = 0·015). In females, serum Mg was associated with total bone mineral content (BMC, β = 0·367, P = 0·004) and robustness (β = 0·393, P = 0·006) at the distal 4 % site, stress–strain index of the polaris axis (β = 0·334, P = 0·009) and robustness (β = 0·420, P = 0·004) at the 14 % diaphyseal site, and BMC (β = 0·309, P = 0·009) and stress–strain index of the polaris axis (β = 0·314, P = 0·006) at the 66 % diaphyseal site pre-IMT. No significant relationships between serum Mg and bone measures were observed in males. Findings suggest that serum Mg may be modulated by Ca/vitamin D intake and may impact tibial bone health during training in female military recruits.

The impact of dietary phosphorus on chronic renal disease in cats, humans and other species is receiving increasing attention. As Ca and P metabolism are linked, the ratio of Ca:P is an important factor for consideration when formulating diets for cats and other animals. Here, we describe a fully randomised crossover study including twenty-four healthy, neutered adult cats, investigating postprandial responses in plasma P, ionised Ca and parathyroid hormone (PTH) following one meal (50 % of individual metabolic energy requirement) of each of six experimental diets. Diets were formulated to provide P at either 0·75 or 1·5 g/1000 kcal (4184 kJ) from the soluble phosphorus salt sodium tripolyphosphate (STPP, Na5P3O10), variable levels of organic Ca and P sources, and an intended total Ca:P of about 1·0, 1·5 or 2·0. For each experimental diet, baseline fasted blood samples were collected prior to the meal, and serial blood samples collected hourly for 6 h thereafter. For all diets, a significant increase from baseline was observed at 120 min in plasma PTH (P < 0·001). The diet containing the highest STPP inclusion level and lowest Ca:P induced the highest peaks in postprandial plasma P and PTH levels (1·8 mmol/l and 27·2 pg/ml, respectively), and the longest duration of concentrations raised above baseline were observed at 3 h for P and 6 h for PTH. Data indicate that Ca:P modulates postprandial plasma P and PTH. Therefore, when formulating diets containing soluble P salts for cats, increasing the Ca:P ratio should be considered.

Phosphorus requirements of reproducing sows were estimated using 24-h urinary P excretion. Thirty-six multiparous sows were fed one of six maize–soybean meal-based diets with total P ranging from 0·40 to 0·80 % in 0·08 % increments with a constant Ca:total P ratio (1·25:1). Diets were fed from day 7·5 ± 1 after breeding until the end of lactation (day 26 ± 1). Urine samples were collected in mid and late gestation (days 77·1 ± 2 and 112·4 ± 1) and early and late lactation (days 4·5 ± 1 and 18·2 ± 1). Phosphorus requirements were estimated using linear and nonlinear regression models. Based on a single 24-h urinary P excretion, estimated daily dietary total P requirements in mid and late gestation were 10·3 g (6·0 g standardised total tract digestible P, STTD P), and estimates for early and late lactation were 31·1 g (16·6 g STTD P) and 40·3 g (22·1 g STTD P), respectively. Plasma P and Ca concentrations were maintained within normal ranges at the estimated levels of P requirements. No differences among treatments were observed for plasma parathyroid hormone (P ≥ 0·06) and bone formation marker (P ≥ 0·16). In lactation, bone resorption marker decreased (P ≤ 0·001) as sows consumed more P. Among the analysed variables, urinary P was the most sensitive response to changes in dietary P intake. Urinary P excretion offers a practical method to estimate P requirements in sows. Our recommended daily total P requirements are 10·3 g for gestation and 35·7 g for lactation.

The coronavirus disease 2019 (COVID-19) pandemic has generated high interest in factors modulating risk of infection, disease severity and recovery. Vitamin D has garnered interest since it is known to modulate immune function and vitamin D deficiency is associated with increased risk of respiratory infections and adverse health outcomes in severely ill patients. There are no population representative data on the direct relationship between vitamin D status and severe acute respiratory syndrome coronavirus 2 infection risk and severity of COVID-19. Data from intervention studies are limited to four studies. Here we summarise findings regarding vitamin D status and metabolism and their alterations during severe illness, relevant to COVID-19 patients. Further, we summarise vitamin D intervention studies with respiratory disease outcomes and in critically ill patients and provide an overview of relevant patient and population guidelines. Vitamin D deficiency is highly prevalent in hospitalised patients, particularly when critically ill, including those with COVID-19. Acute and critical illness leads to pronounced changes in vitamin D metabolism and status, suggestive of increased requirements. This needs to be considered in the interpretation of potential links between vitamin D status and disease risk and severity and for patient management. There is some evidence that vitamin D supplementation decreases the risk of respiratory tract infections, while supplementation of intensive care unit patients has shown little effect on disease severity or length of treatment. Considering the high prevalence of deficiency and low risks associated with supplementation, pro-actively applying current population and patient management guidelines to prevent, monitor and correct vitamin D deficiency is appropriate.

The objectives are to present an updated synopsis on osteosarcopenic adiposity (OSA) syndrome and evaluate the roles of selected micronutrients in its prevention and management. OSA refers to the concurrent deterioration of bone (osteopenia/osteoporosis), muscle (sarcopenia) and adipose tissue expansion. It portrays the most advanced stage in a continuum of body composition disorders. Although OSA has been widely studied involving the populations of different backgrounds, its prevalence is hard to collate because different methodologies and criteria were used for its diagnosis. Another critical health aspect is the presence of low-grade chronic inflammation (LGCI) which contributes to OSA and vice versa. Nutrition is important in the prevention and management of both OSA and LGCI. Although micronutrients act in numerous metabolic and physiological processes, their roles here are presented in relation to OSA (and its components) and LGCI in general and relevant to the COVID-19 pandemic. These include calcium, magnesium, phosphorus, potassium, sodium and vitamins D and K; their interactions, physiological ratios and synergism/antagonism are discussed as well. In conclusion, calcium, magnesium and vitamin D have a profound impact on OSA and its components, and the latter two also on LGCI. Potassium and vitamin K are vital in bone, muscle functioning and possibly adipose tissue modification. Both, but particularly vitamin D, surfaced as important modulators of immune system with application in COVID-19 infections. While both phosphorus and sodium have important roles in bone, muscle and can impact adiposity, due to their abundance in food, their intake should be curbed to prevent possible damaging effects.