This state-of-the-art review aims to highlight the challenges to quantify vitamin activity in foods that contain several vitamers of one group, using as examples the fat-soluble vitamins A and D as well as the water-soluble folate. The absorption, metabolism and physiology of these exampless are described along with the current analytical methodology, with an emphasis on approaches tostandardisation. Moreover, the major food sources for the vitamins are numerated The paper focuses particularly on outlining the so-called SLAMENGHI factors influencing a vitamer's’ abiltiy to act as a vitamin, that is, molecular species, linkage, amount, matrix, effectors of absorption, nutrition status, genetics, host-related factors and the interaction of these. After summarising the current approaches to estimating the total content of each vitamin group, the review concludes by outlining the research gaps and future perspectives in vitamin analysis. There are not standardised methods for the quantification of the vitamers of vitamin A, vitamin D and folate in foods. For folate and beta-carotene, a difference in vitamer activity between foods and supplements has been confirmed, while no difference has been observed for vitamin D. For differences in vitamer activity between provitamin A carotenoids and retinol and between 25OHD and vitamin D international consensus is lacking. The challenges facing each of the specific vitamin community are the gaps in knowledge about bioaccesibility and bioavailability for each of the various vitamers. The differences between the vitamins make it difficult to formulate a common strategy for assessing the quantitative differences between the vitamers. In the future, optimised stationary digestive models and the more advanced dynamic digestive models combined with in-vitro models for bioavailability may more closely resemble in vivo results. New knowledge will enable us to transfer nutrient recommendations into improved dietary advice to increase public health throughout the human life cycle.