Vitamin D deficiency is highly prevalent in the UK (1-2). Low exposure to the sun in winter months, as well as higher risk of deficiency amongst some ethnic minority populations (1), means that fortification of food and beverages remains an important potential route to ensure optimal vitamin D status. However, it is unclear as to whether type of fortified food affects ability to raise vitamin D status. Animal foods (e.g. dairy foods) would be expected to lead to higher vitamin D absorption than would non-animal-based foods (e.g. bread, juice), due to their higher fat content. The primary aim of this systematic review and meta-analysis was to investigate the effectiveness of animal and non-animal-based vitamin D fortified foods on raising serum 25-hydroxyvitamin D (25(OH)D).

The literature search was conducted using PubMed on 23 January 2024. Inclusion criteria were as follows: data on non-pregnant/non-lactating adults or data on children, randomised controlled trial; data for 25(OH)D measurement. Initial search results retrieved 701 publications, and 593 ineligible records were removed. Next, 108 records were screened by title and abstract, with 63 records excluded, for the following reasons: off topic (n=54); pregnant or breastfeeding (n=6); non-human (n=1); preterm infants (n=1) and duration <4 weeks (n=1). After full text eligibility screening, 28 publications remained for systematic review and meta-analysis. Ethical approval was not required as this was a literature review.

The end point data meta-analysis showed (for all studies combined) a significant increase in 25(OH)D (+23.4 (95% CI 17.0, 29.7) nmol/L (24 studies)). For specific food types, results were as follows: ‘animal’ +21.7 (95% CI 14.1, 29.3) nmol/L (17 studies); mixture of ‘animal’ and ‘non-animal’ +26.1 (95% CI 10.8, 41.4) nmol/L (1 study); ‘non-animal’ +28.1 (95% 12.0, 44.2) nmol/L (6 studies).

Contrary to what would be expected, non-animal mode of fortification (e.g. bread, juice) had a similar effect size to animal modes (e.g. dairy), so can be considered equivalent in effectiveness in raising 25(OH)D concentration. Differences in dose, duration and population groups between the non-animal and animal modes (in terms of health and baseline vitamin D status) mean the results should be taken with caution, and future studies where these factors are standardised could be useful to provide further evidence of effectiveness.

The aim of the present study was to assess the seasonal relationship between serum 25(OH)D concentration, lean mass and muscle strength. This was a secondary data analysis of a subgroup of 102 postmenopausal women participating in the 2006–2007 D-FINES (Vitamin D, Food Intake, Nutrition and Exposure to Sunlight in Southern England) study. The cohort was assessed as two age subgroups: <65 years (n=80) and ≥65 years (n=22). Outcome measures included lean mass (DXA), muscle strength (handgrip dynamometry) and serum 25(OH)D concentration (enzymeimmunoassay). Derived outcomes included appendicular skeletal muscle mass (ASM) and relative appendicular skeletal muscle index (RASM). Sarcopenia status was assessed using the European Working Group on Sarcopenia in Older People 2018 criteria. Non-parametric partial correlation using BMI as a covariate was used to evaluate the study aims. There were no statistically significant associations between total lean mass, ASM or RASM and 25(OH)D in any group at any season. There was a trend for handgrip strength to be positively associated with serum 25(OH)D concentration. There was a trend showing a higher prevalence of sarcopenia in women ≥65 years. Sarcopenia status appeared transient for five women. In conclusion, the present study found no significant association between vitamin D status and functional indicators of musculoskeletal health, which were additionally not affected by season.

A multi-disciplinary expert group met to discuss vitamin D deficiency in the UK and strategies for improving population intakes and status. Changes to UK Government advice since the 1st Rank Forum on Vitamin D (2009) were discussed, including rationale for setting a reference nutrient intake (10 µg/d; 400 IU/d) for adults and children (4+ years). Current UK data show inadequate intakes among all age groups and high prevalence of low vitamin D status among specific groups (e.g. pregnant women and adolescent males/females). Evidence of widespread deficiency within some minority ethnic groups, resulting in nutritional rickets (particularly among Black and South Asian infants), raised particular concern. Latest data indicate that UK population vitamin D intakes and status reamain relatively unchanged since Government recommendations changed in 2016. Vitamin D food fortification was discussed as a potential strategy to increase population intakes. Data from dose–response and dietary modelling studies indicate dairy products, bread, hens’ eggs and some meats as potential fortification vehicles. Vitamin D3 appears more effective than vitamin D2 for raising serum 25-hydroxyvitamin D concentration, which has implications for choice of fortificant. Other considerations for successful fortification strategies include: (i) need for ‘real-world’ cost information for use in modelling work; (ii) supportive food legislation; (iii) improved consumer and health professional understanding of vitamin D’s importance; (iv) clinical consequences of inadequate vitamin D status and (v) consistent communication of Government advice across health/social care professions, and via the food industry. These areas urgently require further research to enable universal improvement in vitamin D intakes and status in the UK population.

The present paper reviews published literature on the relationship between dietary protein and bone health. It will include arguments both for and against the anabolic and catabolic effects of dietary protein on bone health. Adequate protein intake provides the amino acids used in building and maintaining bone tissue, as well as stimulating the action of insulin-like growth factor 1, which in turn promotes bone growth and increases calcium absorption. However, the metabolism of dietary sulphur amino acids, mainly from animal protein, can lead to increased physiological acidity, which may be detrimental for bone health in the long term. Similarly, cereal foods contain dietary phytate, which in turn contains phosphate. It is known that phosphate consumption can also lead to increased physiological acidity. Therefore, cereal products may produce as much acid as do animal proteins that contain sulphur amino acids. The overall effect of dietary protein on physiological acidity, and its consequent impact on bone health, is extremely complex and somewhat controversial. The consensus is now moving towards a synthesised approach. Particularly, how anabolic and catabolic mechanisms interact; as well as how the context of the whole diet and the type of protein consumed is important.

Little research has assessed serum 25-hydroxyvitamin D (25(OH)D) concentration and its predictors in Western-dwelling South Asians in a relatively large sample size. This observational, cross-sectional analysis assessed baseline prevalence of 25(OH)D deficiency in UK-dwelling South Asians (aged 40–69 years, 2006–2010) from the UK Biobank Cohort. Serum 25(OH)D measurements were undertaken using the DiaSorin Liaison XL assay. Of 6433 South Asians with a 25(OH)D measurement, using commonly used cut-off thresholds, 55 % (n 3538) had 25(OH)D < 25 nmol/l (severe deficiency) and 92 % (n 5918) had 25(OH)D < 50 nmol/l (insufficiency). Of the participants with a measurement, 20 % (n 1287) had 25(OH)D concentration <15 nmol/l (very severe deficiency). When 824 participants with undetectable (<10 nmol/l) 25(OH)D measurements were included (total n 7257), 29 % (n 2105) had 25(OH)D < 15 nmol/l, 60 % (n 4354) had 25(OH)D < 25 nmol/l and 93 % (n 6749) had 25(OH)D < 50 nmol/l. Logistic regression predictors of 25(OH)D < 25 nmol/l included the following characteristics: being male; Pakistani; higher BMI; 40–59 years old; never consuming oily fish; summer sun exposure <5 h/d, not using a vitamin D-containing supplement, measurement in winter or spring and vegetarianism. In terms of region, median 25(OH)D concentration was 19–20 nmol/l in Scotland, Northern England, the Midlands and Wales. Across Southern England and London, it was slightly higher at 24–25 nmol/l. Our analyses suggest the need for increased awareness of vitamin D deficiency in South Asians as well as urgent public health interventions to prevent and treat vitamin D deficiency in this group.

Vitamin D (vitD) deficiency has been suspected as a risk factor for type 2 diabetes mellitus (T2DM). It has been reported that an inverse relationship exists between vitD status and risk of T2DM. The aim of this study was to investigate whether there is an association between vitD status and glycemic profile and other metabolic parameters among postmenopausal women with T2DM (living in Saudi Arabia). A cross-sectional study was conducted at King Fahad Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia. One thirty six (n = 136) postmenopausal females (age ≥ 50 years) living in Jeddah city, Saudi Arabia, with T2DM were randomly recruited in this study. Anthropometric measures, blood pressure readings and fasting blood samples were obtained fro all study participants. Several biochemical parameters were estimated in fasting serum samples including total 25(OH)D, HbA1c, insulin, glucose, c-peptide and lipid profile. Surrogate markers for insulin resistance were calculated using Homeostasis Model Assessment for insulin resistance and beta cell activity (HOMA-IR, HOMA-β), Quantitative insulin sensitivity check index (QUICK-I) and McAuley's index. VitD deficiency was defined as serum total 25(OH)D level below 20 ng/ml.The Mean (± SD) serum levels of total 25(OH)D were 13.8 ± 8.6 ng/ml with 79% of the study cohort being vitD deficient. Furthermore, serum total 25(OH)D levels were found to be inversely correlated with fasting insulin (r = -0.24, p = 0.029), HOMA-IR (r = -0.24, p = 0.03), and positively correlated with McAuley's index (r = 0.22, p = 0.048) and QUICK-I (r = 0.25, p = 0.024). In conclusion, vitD deficiency is highly prevalent among postmenopausal women with T2DM living in Jeddah, Saudi Arabia. VitD was found to be associated with insulin resistance. Whether vitD supplements are able to improve insulin sensitivity and other parameters in T2DM postmenopausal women should be further investigated.

Vitamin D is vital to bone health and prolonged severe deficiency can lead to rickets in children and osteomalacia/osteoporosis in adults. Vitamin D is an exceptional nutrient in that its main source is exposure of the skin to UV rays, whilst it can also be ingested through diet. This study aimed to investigate the relative contribution of vitamin D supplementation and individual sunlight exposure in raising vitamin D levels, throughout winter, in ethnically identical adult women living in opposite latitudes. Within two parallel placebo-controlled randomized controlled trials (RCT), with identical study designs, 135 Brazilian women, (England, n = 56, 51˚N; Brazil, n = 79, 16˚S), were randomized to receive daily 15 μg vitamin D3 supplements or placebo, for 12 weeks. Oral vitamin D supplementation of 15 μg daily was effective at raising 25-hydroxivitamin D [25(OH)D] concentrations over winter, regardless of latitude, and the response was dependent on baseline vitamin D status. In both latitudes, supplementation prevented the seasonal concomitant increase in plasma parathyroid hormone (PTH) levels. Additionally, the individual UV radiation level was strongly correlated with 25(OH)D concentrations. The research also showed: 1) an optimal vitamin D status for bone health around 70–80 nmol/l; 2) the required UV radiation to achieve this status was 1.5 SED; 3) the vitamin D dietary intakes required to achieve these serum levels were 4.5 μg/d at a low latitude (16˚S) and 37 μg/d at high latitude (51˚N). The strength of these results is the novel analysis that directly links human in vivo individual sunlight radiation, increased vitamin D intake and 25(OH)D status, within two parallel RCTs in opposite latitudes. This study demonstrated that a daily supplement of 15 μg vitamin D3 was an effective strategy to significantly raise vitamin D status throughout the winter months in adult females, with important implications for bone health through the simultaneous lowering of PTH, regardless of latitude. Our data gives a two-fold contribution to the vitamin D field: firstly it will help raise awareness of the risk for vitamin D deficiency in low latitude regions such as most countries in South America as well as amongst South-Americans living in higher latitudes, particularly in the UK; secondly it provides key data for setting appropriate vitamin D recommendations for Brazil (which currently follows US recommendations) as well as for similar latitudes.

Adequate intakes of the B vitamins are essential for health; however there is a lack of data concerning B vitamin intakes in UK dwelling South Asian (SA) groups. We aimed to investigate whether UK SA women meet the LRNI for B vitamins, and whether their intake differs from same-age White Caucasian (WC) women. We used summer 2006 dietary intake data from the Food Standards Agency (FSA) funded D-FINES study (Vitamin D, Food Intake, Nutrition and Exposure to Sunlight in Southern England, project N05064). After removal of over- and under-reporters (energy: BMR ratio < 1 or > 1.6) there were n = 29 SA and n = 146 WC subjects. The two groups did not differ significantly in age and BMI. Overall mean (SD) for age was 50.6 (13.6) years and for BMI was 26.8 (4.8). In SA, 41% were Bangladeshi or Pakistani, 28% were Indian and 31% were of other ethnicity. Independent T-tests, using log transformed data, showed no statistically significant differences for any B vitamin (Bonferroni revised p value: < 0.008). Results were as follows, giving median (IQR): Thiamine (mg) 1.5 (0.5) SA vs 1.4 (0.5) WC; (P = 0.8); Riboflavin (mg) 1.3 (0.5) SA vs. 1.5 (0.6) WC (P = 0.08); Niacin (mg) 30.7 (13.7) SA vs 33.3 (9.8) WC (P = 0.4); B6 (mg) 1.7 (0.5) SA vs 1.9 (0.7) WC (P = 0.2); B12 (micrograms) 2.8 (0.05) SA vs 3.6 (2.5) WC (P = 0.02); Folate (micrograms) 213 (93) SA vs 231 (82) WC (P = 0.8). In terms of percentages below the LRNI: Thiamine 0% SA and 0.7% (n = 1) WC; Riboflavin 0% SA and 1.4% (n = 2) WC; B12 10% (n = 3) SA and 0% WC. For Niacin, B6 and Folate no women in either group were below the LRNI. Overall, there were no ethnic differences in B vitamin intake by ethnicity. There was a trend for a slightly lower B12 intake in SA but this did not reach statistical significance after adjustment for multiple testing. It is of concern that 10% of SA did not meet the LRNI for B12. Of this 10%, the majority were not vegetarian or vegan. The sample size for SA was very small and further research is now required in a larger sample to confirm this finding. The D-FINES study was funded by the UK FSA (N05064). The views expressed are those of the authors alone.

Vitamin D (vitD) deficiency is highly prevalent in the Middle East (including Saudi Arabia) despite the abundance of sunlight. Older individuals in particular are at high risk of being vitD deficient. VitD binding protein (DBP), which acts as a carrier of vitD and its metabolites, has been reported to influence vitD status. In our study we aimed to investigate vitD status among postmenopausal women and its relation to DBP. A cross-sectional study was conducted at the King Fahad Medical Research Center, King Abdulaziz University, Jeddah, Saudi Arabia. Seventy six postmenopausal females (age ≥ 50 years) who were not taking vitD supplementation and who were resident in Jeddah city, were randomly recruited from internal medicine clinics at King Abdulaziz University Hospital. Anthropometric measures, blood pressure, lifestyle history, dietary vitD intake and fasting blood samples were obtained from all study participants. Serum total 25 hydroxy-vitamin D (25(OH)D), DBP, albumin, parathyroid hormone, calcium, phosphate, magnesium and metabolic bone parameters were analysed. VitD deficiency was defined as serum total 25(OH)D level below 30 nmol/L. The mean (± SD) serum level of total 25(OH)D was 46.9 ± 28.9 nmol/L with 36 % of the study population being vitD deficient. Although non-significant, the vitD deficient group had lower DBP and higher dietary vitD intake levels when compared with those with serum vitD > 30nmol/L. In addition, DBP was inversely correlated with vitD dietary intake (r = -0.233, P = 0.046). In conclusion, vitD deficiency is highly prevalent among postmenopausal women living in Jeddah, Saudi Arabia. Intake of a vitD rich food seems to be associated with low DBP levels. Genetic polymorphisms in DBP will be studied in the future to find out a possible explanation for the differences in vitD status and DBP between individuals as well as the concomitant relationship between dietary vitD intake, DBP and serum 25(OH)D levels.

Published studies have suggested a high prevalence of 25-hydroxyvitamin D (25OHD) deficiency in western dwelling South Asians, particularly in women. However, sample sizes have been relatively small with few men. Moreover, South Asians are vastly under-represented in national dietary surveys and further research into 25(OH)D status is needed. The UK Biobank is a cohort of 500,000 individuals; n 6433 are of South Asian ethnicity and have baseline serum 25(OH)D data (2006–2010, aged 40–69 years). Blood draws were spread across the year. Of note, the 25(OH)D measurements were produced using the DiaSorin Liaison XL assay which underestimates 25(OH)D by 4% at 25nmol/L, but overestimates 25(OH)D by 5–10% at ≥ 40nmol/\L(1). We used the commonly used cut-points of < 25nmol/L (deficiency), < 50nmol/L (insufficiency). In women (n 2927), median (IQR) was 24.3 (20.5) nmol/L with 50.4% < 25nmol/L, and 88.6% < 50nmol/L. In men (n 3506), median (IQR) was 21.7 (16.2) with 58.4% < 25 nmol/L and 93.8% < 50 nmol/L. Of concern, 17.8% of women and 21.1% of men had 25(OH)D < 15nmol/L. A Mann Whitney test showed that gender differences were statistically significant (P < 0.0001). In terms of ethnic sub-groups, in the Bangladeshi group (n 207), median (IQR) was 26.1 (14.3) nmol/L with 43.5% < 25nmol/L and 91.3% < 50nmol/L. In the Indian group (n 4792), median (IQR) was 23.8 (19.3) with 52.0% < 25nmol/L and 90.4% < 50nmol/L. Finally, in the Pakistani group (n 1434) median (IQR) was 19.3(14.5) with 65.7% < 25nmol/L and 94.9% < 50nmol/L. A Kruskal Wallis test showed that ethnic subgroup differences were statistically significant (P < 0.0001). To the authors’ knowledge, this is the largest analysis to date of 25(OH)D status in European dwelling South Asians. Deficiency of 25(OH)D was almost universal, with 50% or more not even reaching 25nmol/L. Of great concern, 20% of participants had levels < 15nmol/L which, although not a widely used cut-off point, still represents severe deficiency and likely osteomalacia. Moreover, these results are most probably an underestimation of this societal challenge as the UK Biobank is likely to contain participants that are healthier and more educated than the general population. In conclusion, our analyses suggest the need for urgent public health interventions to prevent and treat vitamin D deficiency in UK South Asians. This research was conducted using the UK Biobank Resource under application number 15168.

Vitamin D deficiency has been commonly reported in elite athletes, but the vitamin D status of UK university athletes in different training environments remains unknown. The present study aimed to determine any seasonal changes in vitamin D status among indoor and outdoor athletes, and whether there was any relationship between vitamin D status and indices of physical performance and bone health. A group of forty-seven university athletes (indoor n 22, outdoor n 25) were tested during autumn and spring for serum vitamin D status, bone health and physical performance parameters. Blood samples were analysed for serum 25-hydroxyvitamin D (s-25(OH)D) status. Peak isometric knee extensor torque using an isokinetic dynamometer and jump height was assessed using an Optojump. Aerobic capacity was estimated using the Yo-Yo intermittent recovery test. Peripheral quantitative computed tomography scans measured radial bone mineral density. Statistical analyses were performed using appropriate parametric/non-parametric testing depending on the normality of the data. s-25(OH)D significantly fell between autumn (52·8 (sd 22·0) nmol/l) and spring (31·0 (sd 16·5) nmol/l; P < 0·001). In spring, 34 % of participants were considered to be vitamin D deficient (<25 nmol/l) according to the revised 2016 UK guidelines. These data suggest that UK university athletes are at risk of vitamin D deficiency. Thus, further research is warranted to investigate the concomitant effects of low vitamin D status on health and performance outcomes in university athletes residing at northern latitudes.

Soldier operational performance is determined by their fitness, nutritional status, quality of rest/recovery, and remaining injury/illness free. Understanding large fluctuations in nutritional status during operations is critical to safeguarding health and well-being. There are limited data world-wide describing the effect of extreme climate change on nutrient profiles. This study investigated the effect of hot-dry deployments on vitamin D status (assessed from 25-hydroxyvitamin D (25(OH)D) concentration) of young, male, military volunteers. Two data sets are presented (pilot study, n 37; main study, n 98), examining serum 25(OH)D concentrations before and during 6-month summer operational deployments to Afghanistan (March to October/November). Body mass, percentage of body fat, dietary intake and serum 25(OH)D concentrations were measured. In addition, parathyroid hormone (PTH), adjusted Ca and albumin concentrations were measured in the main study to better understand 25(OH)D fluctuations. Body mass and fat mass (FM) losses were greater for early (pre- to mid-) deployment compared with late (mid- to post-) deployment (P<0·05). Dietary intake was well-maintained despite high rates of energy expenditure. A pronounced increase in 25(OH)D was observed between pre- (March) and mid-deployment (June) (pilot study: 51 (sd 20) v. 212 (sd 85) nmol/l, P<0·05; main study: 55 (sd 22) v. 167 (sd 71) nmol/l, P<0·05) and remained elevated post-deployment (October/November). In contrast, PTH was highest pre-deployment, decreasing thereafter (main study: 4·45 (sd 2·20) v. 3·79 (sd 1·50) pmol/l, P<0·05). The typical seasonal cycling of vitamin D appeared exaggerated in this active male population undertaking an arduous summer deployment. Further research is warranted, where such large seasonal vitamin D fluctuations may be detrimental to bone health in the longer-term.

Vitamin D is a unique nutrient. First, it acts as a pro-hormone and secondly, the requirement for vitamin D can be met by both endogenous synthesis from sunlight and by dietary sources. This complicates the determination of dietary requirements for vitamin D, which along with the definition of optimal vitamin D status, have been highly controversial and much debated over recent years. Adolescents are a population group at high risk of low vitamin D status, which is concerning given the important role of vitamin D, and calcium, in promoting normal bone mineralisation and attainment of peak bone mass during this rapid growth phase. Dietary vitamin D recommendations are important from a public health perspective in helping to avoid deficiency and optimise vitamin D status for health. However limited experimental data from winter-based dose–response randomised trials in adolescents has hindered the development of evidence-based dietary requirements for vitamin D in this population group. This review will highlight how specifically designed randomised trials and the approach adopted for estimating such requirements can lead to improved recommendations. Such data indicate that vitamin D intakes of between 10 and about 30 µg/d may be required to avoid deficiency and ensure adequacy in adolescents, considerably greater than the current recommendations of 10–15 µg/d. Finally this review will consider the implications of this on public health policy, in terms of future refinements of vitamin D requirement recommendations and prioritisation of public health strategies to help prevent vitamin D deficiency.

Seafood intake in pregnancy has been positively associated with childhood cognitive outcomes which could potentially relate to the high vitamin D content of oily fish. However, whether higher maternal vitamin D status (serum 25-hydroxyvitamin D (25(OH)D)) in pregnancy is associated with a reduced risk of offspring suboptimal neurodevelopmental outcomes is unclear. A total of 7065 mother–child pairs were studied from the Avon Longitudinal Study of Parents and Children cohort who had data for both serum total 25(OH)D concentration in pregnancy and at least one measure of offspring neurodevelopment (pre-school development at 6–42 months; ‘Strengths and Difficulties Questionnaire’ scores at 7 years; intelligence quotient (IQ) at 8 years; reading ability at 9 years). After adjustment for confounders, children of vitamin D-deficient mothers (<50·0 nmol/l) were more likely to have scores in the lowest quartile for gross-motor development at 30 months (OR 1·20; 95 % CI 1·03, 1·40), fine-motor development at 30 months (OR 1·23; 95 % CI 1·05, 1·44) and social development at 42 months (OR 1·20; 95 % CI 1·01, 1·41) than vitamin D-sufficient mothers (≥50·0 nmol/l). No associations were found with neurodevelopmental outcomes, including IQ, measured at older ages. However, our results suggest that deficient maternal vitamin D status in pregnancy may have adverse effects on some measures of motor and social development in children under 4 years. Prevention of vitamin D deficiency may be important for preventing suboptimal development in the first 4 years of life.

The role of vitamin D in supporting the growth and maintenance of the skeleton is robust; with recent research also suggesting a beneficial link between vitamin D and other non-skeletal health outcomes, including immune function, cardiovascular health and cancer. Despite this, vitamin D deficiency remains a global public health issue, with a renewed focus in the UK following the publication of Public Health England's new Dietary Vitamin D Requirements. Natural sources of vitamin D (dietary and UVB exposure) are limited, and thus mechanisms are needed to allow individuals to achieve the new dietary recommendations. Mandatory or voluntary vitamin D food fortification may be one of the mechanisms to increase dietary vitamin D intakes and subsequently improve vitamin D status. However, for the food industry and public to make informed decisions, clarity is needed as to whether vitamins D2 and D3 are equally effective at raising total 25-hydroxyvitamin D (25(OH)D) concentrations as the evidence thus far is inconsistent. This review summarises the evidence to date behind the comparative efficacy of vitamins D2 and D3 at raising 25(OH)D concentrations, and the potential role of vitamin D food fortification as a public health policy to support attainment of dietary recommendations in the UK. The comparative efficacy of vitamins D2 and D3 has been investigated in several intervention trials, with most indicating that vitamin D3 is more effective at raising 25(OH)D concentrations. However, flaws in study designs (predominantly under powering) mean there remains a need for a large, robust randomised-controlled trial to provide conclusive evidence, which the future publication of the D2–D3 Study should provide (BBSRC DRINC funded: BB/I006192/1). This review also highlights outstanding questions and gaps in the research that need to be addressed to ensure the most efficacious and safe vitamin D food fortification practices are put in place. This further research, alongside cost, availability and ethical considerations (vitamin D3 is not suitable for vegans), will be instrumental in supporting government, decision-makers, industry and consumers in making informed choices about potential future vitamin D policy and practice.