Bioavailability dietary factors

The importance of dietary or endogenously synthesized vitamin D has long been recognized as a primary factor influencing the bioavailability of calcium. Some of the most exciting biochemical-nutritional research in recent years has been devoted to determining the mechanisms involved in vitamin D-calcium interactions. This research has been well reviewed in other publications. The objective of the symposium upon which this book is based was to review some of the other lesser-known dietary factors that appear to have an impact on the bioavailability of calcium. 

Many other dietary factors have been reported to affect calcium bioavailability. Phytate, fiber, cellulose, uronic acids, sodium alginate, oxalate, fat (only in the presence of steatorrhea), and alcohol have been reported to decrease calcium bioavailability (15). Lactose and medium chain triglyceride increase it (15). FTuoride also affects calcium retention primarily by stimulating bone formation thereby decreasing calcium excretion (33-38). The effects of fluoride on calcium utilization have been variable (34,38,39). 

Bone is very sensitive to dietary factors such as the amount of calcium present in the diet and the availability of that calcium when all other nutrients are present in adequate amounts (46, 47). This is especially true of the growing animal which is utilized in most bioavailability studies. Adult animals, however, may also be used. Krook et al (48) caused osteoporosis in adult dogs in 42 weeks by feeding a low-calcium high-phosphorus diet. The bones were radiologically normal after 28 weeks of calcium repletion (48). The ash contents of the vertebral bones of these dogs were much more responsive to dietary calcium and phosphorus manipulation than were the humeri and femora (48). 

Manganese is an essential nutrient for humans with a daily estimated adequate safe and daily dietary intake of 2.5 to 5.0 mg (1). Yet trace mineral nutriture depends not only upon dietary intake, but also upon availability for absorption. Currently, little is known regarding the influence of dietary factors on the absorption of manganese. Thus the intent of these studies was to (a) develop a test that would readily measure Mn bioavailability in humans and (b) utilize this test to determine the influences of various dietary factors on Mn bioavailability. 

Impact of dietary factors on manganese bioavailability and on manganese nutritional status have not been extensively investigated. The objective of the current project was to determine effects of... 

Many factors have been identified as influencing the absorption of iron. In addition to changes within the host which affect iron absorption and the form of the iron salt, various dietary constituents which may increase or decrease iron bioavailability have also been studied. As diets become more plant product oriented and less iron is provided by animal products, the occurrence of these other dietary factors is also likely to change. Factors which have been implicated include the following amount of heme iron, ascorbic acid level, dietary protein,... 

Despite the fact that a plethora of dietary factors could, and will, affect the absorption characteristics of phytochemicals, this area has not been systematically explored. One reason might be the complexity of dietary factors and their interactions that could affect absorption. A nonexhaustive list would include the volume and composition of the food consumed, pH, caloric density, viscosity, nutrients (carbohydrates, protein, fat, fibers), alcohol, caffeine, and the presence of other phytochemicals. Such dietary factors affect the functional status, motility, and acidity of the gastrointestinal tract in a complex manner and modify the physicochemical properties, formulation, and dissolution characteristics of the compound of interest. Calcium in dairy products, for example, has the potential to chelate tetracyclines and fluoroquinolones and, thereby, reduce their bioavailability and biological activity [31]. 

Although certain macroalgae are rich in vitamins, the bioavailability of these compounds has not been studied sufficiently yet, so there is not enough data to clarify this problem for all vitamins satisfyingly. Bioavailability is influenced by several factors as follows characteristics of the food source, location of the vitamin in the plant source, particle size, the presence of other influencing dietary components and interactions with other dietary factors, the type and extent of processing (Rock et ah, 1998). 

More studies should be carried out in what concerns anthocyanin transport across biological membranes. There are studies aimouncing neuroprotective effects of anthocyanin-rich foods, but there is a gap in the knowledge concerning, for example, anthocyanin (and metabolites) transport across blood-brain barrier. On top of this, it is urgent to know dietary factors able to modulate anthocyanin bioavailability, helping health professionals to make dietary recommendations. These recommendations will be relevant for a healthy life but also to alert medical doctors as to possible pharmacological interactions with anthocyanins. 

Van het Hof, K.H. et al., Dietary factors that affect the bioavailability of carotenoids,... 

WISEMAN H (1999) The bioavailability of non-nutrient plant factors dietary flavonoids and phyto-oestrogens. Proc Nutr Soc. 58 (1) 139-46. 

The concept of bioavailability was developed to explain the difference between the total amount of mineral in a food and the amount which was used by the individual consuming the food. Over the past sixty years or more, there have been numerous studies related to dietary calcium requirements and bioavailability (1,2). As a result, much is known about non-calcium food components which influence the absorption and utilization of dietary calcium under experimental conditions. What now is lacking is a detailed knowledge of how these factors interact with calcium under normal conditions of ingestion in meals. 

Bioavailability of Ca2+ is affected by numerous physiological conditions, including age, sex, genetic make-up, stress, hormonal status, health status, and nutritional habits. In addition to these intrinsic factors, certain dietary components, such as fiber and oxalate, form insoluble complexes with Ca2+ and interfere with its absorption. Another putative culprit in this category is phytic acid. 

In the event of dietary Ca abundance, Ca in excess of adequate circulating concentrations is deposited in the skeleton. This occurs to the extent of the body s ability to store Ca, and any excess beyond this threshold is excreted. Accrual of Ca into bone is governed by such factors as dietary intake (including the absorption, bioavailability, utilization of nutrients and minerals, and other dietary constituents that influence absorption or retention), calciotropic hormones, genetic potential, lifestyle factors, life stage, general health, and the adaptive response to physical/mechanical stimuli within the constraints of metabolic economy. 

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