08 March 2011
The intake of preformed vitamin A from animal products is not sufficient in parts of the population in Europe, the U.S. and Asia. The vitamin A precursor beta-carotene therefore has an important function in providing for an adequate supply of total vitamin A, international carotenoid experts state in a published consensus answer (1).
Vitamin A is essential for normal growth and development, immune system, vision and other functions in the human body. In situations such as pregnancy and lactation, vitamin A plays a particularly important role in the healthy development of the child, and an increase in vitamin A (retinol) intake has been recommended under these conditions. However, surveys undertaken in several countries suggest that vitamin A intake patterns vary considerably across Europe, the U.S. and Asia. National survey data show that the intake of preformed vitamin A (retinol) – as such only present in animal products (especially liver) – is often critically low and does not meet the recommendations. Groups especially at risk of inadequate vitamin A supply are pregnant and lactating women, newborns, children with frequent infections, young women, the elderly and people who avoid animal-derived foods.
National Consumption Surveys indicate that beta-carotene – as a vitamin A precursor – contributes significantly to balance inadequate vitamin A supply in large parts of the population. However, European, U.S. and Asian studies show that a substantial part of the population does not reach the recommendation for beta-carotene necessary to compensate the low vitamin A intake from sources containing preformed vitamin A in the regular diet. Recent evidence has shown that suboptimal levels of vitamin A and beta-carotene, even well above those causing clinical deficiency syndromes, can be risk factors for chronic diseases.
The bioavailability of beta-carotene is influenced by numerous factors. In addition to food-related factors, such as food matrix, food processing, dosage, fat in the meal, and dietary fibers, the bioavailability of beta-carotene depends on consumer-related factors including vitamin A status, gut integrity and genetic variations. Recent research on female subjects has shown that almost 50% of the population have a genetic variation which reduces their ability to produce sufficient amounts of vitamin A from beta-carotene. Studies indicate that younger women carrying the genetic variation are at particular risk as they tend to eat not enough vitamin A-rich foods relying heavily on the beta-carotene form of the nutrient.
It is apparent from a variety of studies that beta-carotene is essential in striving for the recommended vitamin A intake. In cases of a poor vitamin A status due to low intake of preformed vitamin A, the current recommendations for beta-carotene in the range of 2–4 mg per day still might not sufficiently correct the individual vitamin A status. In their consensus answer the experts conclude that ignoring inter-individual differences in the ability to convert beta-carotene to vitamin A and assuming that intakes of preformed retinol do not change, it should be ensured that the current recommended intakes of beta-carotene are attained. At the same time, people with an inadequate intake of preformed vitamin A should increase consumption to 7 mg per day, based on a realistic and now in the scientific community generally accepted conversion efficiency of 1:12 (12 milligrams of beta-carotene are necessary to form one milligram of vitamin A). This should ensure that at least 95% of the population meet the recommended intakes of total vitamin A. Individuals with reduced conversion efficiencies due to a genetic variability in beta-carotene metabolism might need to increase their daily intakes even further. This is currently being investigated.
According to the experts, there is no difference in function between naturally occurring and chemically synthesized beta-carotene, whereas there is a difference in bioavailability from different food sources. In humans, the predominant molecular type is ‘all-trans beta-carotene’, used for most dietary supplements and fortified foods; it is absorbed preferentially compared to other forms. As the general population is not obtaining sufficient beta-carotene from fruit and vegetables alone, foods fortified or colored with beta-carotene and dietary supplements are important contributors to the daily supply of vitamin A.
Dr. Georg Lietz, School of Agriculture, Food and Rural Development (AFRD), University of Newcastle, Newcastle upon Tyne, UK:
"In the U.K., 50% of men and 49% of women do not meet current national recommendations for preformed vitamin A when other provitamin A sources are not taken into consideration. Thus, people with reduced ability to convert provitamin A sources to active vitamin A could be susceptible to wide-ranging health risks. This is especially important since recent research indicates that approximately 40% of all Europeans possess a gene variant that restricts the amount of beta-carotene their bodies can utilize and convert into vitamin A. If the gene-related restrictions on the utilization of beta-carotene would be taken into account, then the daily recommendation might need to be significantly higher, or alternatively, these individuals might have to increase their preformed vitamin A intake from animal sources or supplements."
Prof. Dr. David Thurnham, Northern Ireland Centre for Diet and Health, University of Ulster, Coleraine, UK:
“Based on numerous studies it is evident that parts of the U.K. population do not meet the recommendation for vitamin A with dietary sources for preformed vitamin A (e.g., liver). To fill the gap between the low intakes from sources containing preformed vitamin A, adequate amounts of beta-carotene must be supplied. Foods fortified or colored with beta-carotene and dietary supplements are important contributors to the daily supply of vitamin A.”
Prof. Dr. A. Catharine Ross, Department of Nutritional Sciences, Pennsylvania State University, University Park, USA:
“A recent U.S. report found large parts of the population to have insufficient intakes of vitamin A. A large quantity of vitamin A is consumed in the form of its precursor beta-carotene. However, the current beta-carotene intake does not fill the gap of low vitamin A intakes from diet. To bridge the gap, increased amounts of beta-carotene and vitamin A must be supplied by regular diet and fortified food or dietary supplements if needed.”
Prof. Dr. Guang-Wen Tang, USDA Human Nutrition Research Center on Aging, Friedman School of Nutrition Science and Policy, Tufts University, Boston, USA:
“Recent research indicates that many people possess a gene variant that restricts the amount of beta-carotene their bodies can utilize, for example convert into vitamin A. If the gene-related restrictions on the utilization of beta-carotene are taken into account, then the current daily intake recommendations need to be increased to reach adequate vitamin A supply.”
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