The OPTIFORD project's work plan is divided into five studies:

1. Adolescent Girls – Impact of vitamin D on bone accretion.

This work package is designed to provide new knowledge on the importance of vitamin D intake at the period of maximum bone growth, which happens around age 12-13 at time of menarche in girls. It will address the following key question, which has major implications for recommendations and fortification policies since a considerable part of European adolescents has low vitamin D status during winter:

To what extent will increased vitamin D intake improve bone accretion in normal young girls?

2. The Elderly – Determination of lowest beneficial dose.

A large part of the elderly need an increased vitamin D supply and fortification of a suitable food could be effective in this respect. The aim of this Work Package is to evaluate the effectiveness of fortification strategies in this age group. A major difficulty is that elderly are eating less than the younger raising the question:

Can elderly benefit from fortification at levels which are realistic without putting younger people at risk of toxicity? And what is the lowest effective dose of vitamin D that beneficially affects calcium metabolism?

3. Muslim Families – Vitamin D, bone accretion and lack of sun exposure.

This work package is designed to provide new knowledge on a large population group living in a traditional Islamic cultural pattern in Europe and which is at greatest risk of vitamin D deficiency. The dosage level of supplemental vitamin D to correct insufficient sun exposure has not been established in these groups. This work package will address the following key questions:

What is the dose necessary to replenish vitamin D status when sun exposure is minimal and are females more prone to vitamin D deficiency than males in these families? To what extent will increased vitamin D intake beneficially affect bone mineral density?

4. The Five Countries - Contribution of diet and sun exposure for vitamin D status across Europe

This Work Package is designed to assess: The influence of dissimilarities in environmental and behaviouristic patterns on supply levels of vitamin D between different European countries. It will consist of a one year long prospective observational study across five European countries in two age groups: adolescents and elderly. The seasonal variation in vitamin D status and PTH will be related to solar exposure and oral intake of vitamin D, including the contributions of fortification and supplements. The participating countries cover the large variation within Europe in dietary habits (fish consumption is three times higher in Southern Europe compared to Northern Europe), in fortification policies, number of supplementation users and "sun-richness".

5. Fortification of Bread – Bioavailability of vitamin D from a non-fatty food.

In order to increase vitamin D intake the selection of foods enriched with vitamin D should be broadened, as recommending supplementation is not always a feasible strategy. Presently fatty foods, such as margarine, milk and vegetable oils are used as the fortified vehicle. Fortifying a commonly consumed non-fatty food would represent a major innovation. Thus, the primary aim of this Work Package is: To develop vitamin D fortified bread and to determine the bioavailability of the incorporated vitamin, as well as the acceptability to the consumer.