Folates bioavailability, absorption

Milk is an excellent source of calcium, phosphorus, riboflavin (vitamin B2), thiamine (vitamin Bl) and vitamin B12, and a valuable source of folate, niacin, magnesium and zinc (Food Standards Agency, 2002). In particular, dairy products are an important source of calcium, which is vital for maintaining optimal bone health in humans (Prentice, 2004). The vitamins and minerals it provides are all bioavailable (i.e. available for absorption and use by the body) and thus milk consumption in humans increases the chances of achieving nutritional recommendations for daily vitamins and mineral intake (Bellew et al., 2000). 

Following oral administration leucovorin is rapidly absorbed and expands the serum pool of reduced folates. Oral absorption of leucovorin is saturable at doses greater than 25 mg. The apparent bioavailability of leucovorin was 97% for 25 mg, 75% for 50 mg, and 37% for 100 mg. 

Folacin bioavailability varies among the vitamers (120,125). Folic acid is more readily available than the naturally occurring food folates but may be less available from fortified foods than in aqueous solution or tablet form. Food folates have been reported to be 30-80% as available as folic acid. Folacin availability, absorption, and metabolism were recently reviewed (20,120,122). 

An unanswered question in this type of protocol is the bioavailability of the ingested folate. If one assumes a fractional absorption of 0.67 for total ingested folate (i.e., labeled + dietary), this model yields estimates for the masses of pools 1 and 6 of 2.9S and 36.S mg, respectively. Thus, the bioavailability of ingested folate is a critically important factor in controlling the in vivo pool sizes and, thus, the nutritional status of the individual. 

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