A scoping review of the public health impact of vitamin D-fortified dairy products for fracture prevention

To measure the public health impact of dairy products, different outcomes could be used including the number of fractures prevented, the number of life years saved, the number of quality-adjusted life years (QALY) or disability-adjusted life years (DALY) gained or in money (referred as cost-of-illness study). QALY is an attractive outcome measure combining quality of life (morbidity) and quantity of life (mortality) in a single metric and is also the outcome used in cost-utility analysis (13). DALY is another measure of disease burden, expressed as the number of years lost due to disability or early death.

To assess the economic impact of an intervention, economic evaluations are conducted with the aim to compare the costs and outcomes of two or more health interventions (13). We distinguish between a cost-effectiveness analysis (CEA) where the outcome is expressed in natural units (such as the number of fractures prevented) and a cost-utility analysis (CUA) where QALY is used as outcome. The latter is often preferred since it allows comparisons between different interventions and diseases. The results of an economic evaluation (CUA or CEA) are expressed in terms of incremental cost-effectiveness ratio (ICER) which is defined as the difference in cost between the intervention and the comparator divided by their differences in outcomes. An ICER represents the additional cost of the intervention per unit of effect (e.g. cost per fractures prevented, or cost per QALY gained). If the ICER is lower than a certain threshold representing the maximum decision makers that are willing to pay for a unit of effect, the intervention is considered cost-effective. In CEA, no thresholds are generally available; for CUA, there is no consensus on the cost per QALY gained that represents good value for money. Thresholds in the range of €30,000–€45,000 are the most commonly used for defining cost-effectiveness. The World Health Organization has suggested a value of three times the gross domestic product (GDP) per capita as the DALY value to be used as cost-effectiveness threshold in developed countries. Borgström et al. (14) have suggested a threshold for QALY equal to two times the GDP per capital for industrialized countries. This threshold has been used for defining fracture risk thresholds in several countries (15, 16).

A total of 125 articles were identified through the PubMed search, of which a total of 7 articles met our inclusion criteria (17‐23) (see flow chart on Fig. 1). The study characteristics are included in Table 1.

Five of these studies (17, 18, 21‐23) assessed the public health and/economic impact of dairy products (also called vitamin D-fortified dairy products, vitamin D and calcium food fortification, vitamin D-rich dairy products) while two studies (19, 20) assessed the impact of calcium and vitamin D supplementation without mentioning the specific use of dairy products. Four studies assessed the public health impact of dairy products in terms of costs, number of fractures prevented, life years gained, DALY gained or QALY gained (17, 21‐23) and all studies except the study of Lotters assessed the cost-effectiveness of dairy products (or calcium and vitamin D supplementation). Four studies estimated the cost per QALY gained of dairy products (17, 19‐21), one assessed the cost per fracture prevented and cost per life year gained (17), and one study used a benefit-cost ratio comparing costs and fractures prevented (23).

Three studies were conducted in Belgium (17, 18, 20), one in France (21), one in Germany (23), one in Norway (19) and one study included three countries (i.e. Sweden, the Netherlands and France) (22). All studies used a model to simulate the public health or economic impact. Most studies (17, 18, 20, 21) used a previously validated Markov microsimulation model that has frequently been used to assess the cost-effectiveness of osteoporosis interventions (24).

Different strategies were used by the authors to model the public health impact of dairy products. Ethgen et al. (17) assessed the public health impact of appropriate daily intake during the remaining lifetime of a cohort, while Hiligsmann et al. (21) assumed an appropriate intake for 1 year and assessed the lifetime implications of this 1-year appropriate intake. In Sandmann et al. (23), the effect of a voluntary food fortification programme was assessed (assuming an 82% adherence level to the programme). Lotters et al. (22) assessed the potential impact of increasing dairy foods consumption in people with an inadequate calcium intake. Hagen et al. (19) assessed the impact of cardiovascular effects on the cost-effectiveness of calcium and vitamin D supplementation.

The effect of dairy products on the risk of fractures was derived from systematic reviews. Three studies (17, 18, 20) used the results of a literature search of articles describing the efficacy of vitamin D in combination with calcium in terms of fracture risk reduction (20). The three most recent studies (19, 21, 23) used the effect of calcium and vitamin D supplementation on fracture risk from a Cochrane review (1).

Four studies assessed the public health impact of dairy products (18, 21‐23) (see Table 2).

First, Lotters et al. (22) estimated that the number of hip fractures that may potentially be prevented each year with additional dairy products was 2023 in France, 455 in Sweden and 132 in the Netherlands. The yearly number of DALY lost was estimated at 6263 for France, 1246 for Sweden, and 374 for The Netherlands. The corresponding total costs that might potentially be avoided were estimated at €129 million, €34 million, and €6 million, in these countries, respectively.

Second, Ethgen et al. (17) estimated the projected health and economic impact of the recommended dairy daily intake versus the absence of appropriate intake in Belgium. The authors estimated that 30,376 fractures and 6605 life years could be saved for an appropriate dairy intake over the remaining lifetime of all women aged over 50 years. In men, the number of fracture avoided and life years gained were estimated at 16,105 and 6144 respectively.

Third, Sandmann et al. (23) estimated that the implementation of a vitamin D and calcium food fortification programme would lead to annual net cost savings of €315 million and the prevention of 36,705 fractures in the German female population aged 65 years and older.

Fourth, in the general French population aged over 60 years, Hiligsmann et al. estimated the lifetime health impacts of the recommended intake of dairy products in the general French population for 1 year (2015) (21). The recommended intake of dairy would reduce the total lifetime number of fractures by 64,932, of which 46,472 and 18,460 would occur in women and men, respectively. In particular, 19,500 hip fractures could be prevented. Dairy products would also result in 32,569 QALYs and 29,169 life years gained.

In summary, all these studies reported a substantial public health benefit of dairy products in terms of fractures prevented as well as in life years, QALY or DALY gains. Direct comparison of studies is difficult given the variety in methodology and outcomes used. We could however mention that the benefits in terms of fractures ranged from 132 hip fractures per year in the Netherlands with additional dairy products to a lifetime gained of 63,392 fractures in France for 1 year of the recommended intake of dairy products.

Six studies assessed the cost-effectiveness of dairy products (17‐21, 23) (see Table 3).

The studies assessing the cost-effectiveness of calcium and vitamin D supplementation without referring to dairy products suggested that that the intervention is cost-effective in populations above 60 years with cost per QALY gained lower than €45,000 (19, 20). The study of Hagen et al. (19) revealed however that the potential cardiovascular effects of calcium and vitamin D supplementation could alter this conclusion.

The studies assessing directly the cost per QALY gained of dairy products suggested that the intervention is generally cost-effective in the general population aged above 70 years (21) or 80 years (17, 18) and from the age of 60 years in population at increased risk of fractures. The study of Sandmann et al. even suggested that the implementation of a vitamin D and calcium food fortification programme is cost-saving (i.e. intervention cost lower than saved costs resulting from less fractures) in the German female population above the age of 65 years.