Challenges to Quantify Total Vitamin Activity: How to Combine the Contribution of Diverse Vitamers?

Abstract

This state-of-the-art review aims to highlight the challenges in quantifying vitamin activity in foods that contain several vitamers of a 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 examples are described along with the current analytical methodology, with an emphasis on approaches to standardization. Moreover, the major food sources for the vitamins are numerated. The article focuses particularly on outlining the so-called SLAMENGHI factors influencing a vitamer's’ ability 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 summarizing 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 no standardized methods for the quantification of the vitamers of vitamin A, vitamin D, and folate in foods. For folate and β-carotene, a difference in vitamer activity between foods and supplements has been confirmed, whereas no difference has been observed for vitamin D. For differences in vitamer activity between provitamin A carotenoids and retinol, and between 25-hydroxyvitamin D and vitamin D, international consensus is lacking. The challenges facing each of the specific vitamin communities are the gaps in knowledge about bioaccessibility 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, optimized stationary digestive models and the more advanced dynamic digestive models combined with in vitro models for bioavailability could 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.

Natural Vitamin D in Food: To What Degree Does 25‐Hydroxyvitamin D Contribute to the Vitamin D Activity in Food?

“…Through the years a factor of five have been used to convert content of 25-OHD3 to content of vitD3 (10,47), and also at the moment used in Food Databanks in UK and Denmark. In reviews for vitamin D in foods (7,23,48,49) and for the appropriate choice of vitamin D source for supplement (21) there are no documentation identified that content of 25-OHD3 is five times more efficient than content of vitD3.…”

“…Since then, the chemical analytical procedure for quantification of vitD3 and vitD2 (vitD) in foods has been continuously improved and extended to include 25-OHD. For vitD, a standardized method is available, but no standardized method is available for 25-OHD in foods (7). Analytical methods for quantification of vitD and 25-OHD have been published, in which the steps in the analytical procedure today are similar as in the1960s.…”

“…In human, it is ethically not possible to perform such studies, thus other endpoints and in-vitro models have been used. A recent review aimed to evaluate the studies investigating dietary intake of vitamin D from foods, and concluded that vitD3 and 25-OHD3 in foods should be regarded as equal in the estimation of vitamin D activity in foods (7).…”

“…For vitD, a standardized method is available, but no standardized method is available for 25OHD in food. ( 7 ) Analytical methods for quantification of vitD and 25OHD have been published, in which the steps in the analytical procedure today are similar to those of the 1960s. They consist of saponification, liquid–liquid extraction, and an extra clean‐up step that is necessary for the analysis of vitamin D vitamers in food.…”

“…A recent review aimed to evaluate the studies investigating dietary intake of vitamin D from food, and concluded that vitD3 and 25(OH)D 3 in food should be regarded equally in the estimation of vitamin D activity in food. ( 7 )…”