Indices of vitamin status in man: An urgent need of functional markers

Olestra dose response on fat-soluble and water-soluble nutrients in the pig

Groups of weanling pigs were fed a purified diet containing graded concentrations of olestra ranging from 1.1 to 7.7% (wt/wt) and the NRC's requirements for micronutrients for 12 wk. Each group consisted of 12 pigs, with the exception of the control group, which had 20, with equal numbers of females and castrated males. The purpose of the study was to determine the dose-response effects of olestra on fat-soluble vitamins and selected water-soluble micronutrients. At wk 0, 4, 8 and 12, hematology, clinical chemistry and blood concentrations of vitamins A, E, K and B12, and 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, folate, calcium, iron, zinc and adipose concentration of vitamin E were measured. Cumulative weight gain and feed efficiency were determined weekly. Prothrombin time was measured weekly for the control group and the groups fed 5.5 or 7.7% olestra, and monthly for other groups. Liver concentrations of vitamins A, E, and B12 and iron and bone concentrations of calcium, phosphorus, zinc and ash were measured for 12 pigs killed at wk 0 and for all animals at wk 12. By wk 12, the pigs were eating from 20 to 155 g/d of olestra. Olestra did not affect the pigs' growth or feed efficiency, indicating that the digestion and absorption of macronutrients were unaffected. Olestra reduced tissue concentrations of vitamin A, vitamin E and 25-hydroxyergocalciferol in a dose-responsive manner but did not affect prothrombin time. Olestra had no effect on the status of folate, vitamin B12, zinc or iron. Statistically reduced liver concentrations of vitamin B12 and iron in groups fed 5.5 or 7.7% olestra and a significant trend in bone ash content with olestra intake were possibly due to the poor vitamin A and/or vitamin E status of the pigs.

Thiamin, riboflavin and vitamin B6: impact of restricted intake on physical performance in man

OBJECTIVE

A combined marginally deficient status of thiamin, riboflavin, vitamin B6 and vitamin C may affect physical performance, but the relative contribution of each vitamin can only be speculated. In a previous study we did not find any effect of restricted intake of vitamin C individually. Therefore, the functional effect of restriction of thiamin, riboflavin or vitamin B6, individually or in conjunction, was investigated.

METHODS

A double-blind, 2 x 2 x 2 complete factorial experiment on the effects of thiamin, riboflavin and vitamin B6 restriction on physical performance was executed with 24 healthy men. During 11 weeks of low vitamin intake, the subjects were given a daily diet of regular food products providing no more than 55% of the Dutch Recommended Dietary Allowances (RDA) for thiamin, riboflavin and vitamin B6. Other vitamins were supplemented at twice the RDA level.

RESULTS

In vitamin-restricted subjects, blood vitamin levels, erythrocytic enzyme activities and urinary vitamin excretion decreased and in vitro erythrocytic enzyme stimulation increased. Short-time vitamin restriction had no harmful effects on health. A significant overall decrease was observed in aerobic power (VO2-max; 11.6%), onset of blood lactate accumulation (OBLA; 7.0%) and oxygen consumption at this power output (VO2-OBLA; 12.0%), peak power (9.3%), mean power (6.9%) and related variables (p < 0.01). However, the observed performance decrements could not be attributed to marginal deficiency for any of the vitamins studied.

CONCLUSION

The absence of vitamin-specific effects on performance decrements due to thiamin, riboflavin and vitamin B6 restriction suggests quantitatively similar but non-additive effects of these B-vitamins on mitochondrial metabolism.

Vitamin C status in elderly women: a comparison between women living in a nursing home and women living independently

The vitamin C status in blood fractions in 135 elderly women aged 65 years and older was studied within the framework of the Dutch Nutrition Surveillance System. Mean (+/- standard deviation) vitamin C intake (mg/day) was lower among women living in a nursing home (54 +/- 27 mg/day) than among women living in service flats (97 +/- 55 mg/day) and women living independently (132 +/- 44 mg/day). (Service flats are apartments in which the rent includes housekeeping and, when ordered, meal service.) Marginal vitamin C values (< 23 mumol/L) in blood fractions and even levels as low as those found in clinical scurvy (< 11 mumol/L) were frequently observed. In the nursing home, 35% of the women had plasma vitamin C values below 11 mumol/L, and 23% had values between 11 and 23 mumol/L. Blood levels were not significantly affected by age, smoking status, or use of particular drugs but were strongly (r = .47 or, after logarithmic transformation, r = .64) associated with daily intake of vitamin C. Low intake of vitamin C resulted from an overall low food consumption and selective restriction of food products rich in vitamin C. Vitamin C losses caused by food preparation practices and distribution in the nursing home's catering system reduced actual vitamin C intake levels but these losses were not substantially greater than those that are assumed to occur as a result of preparation practices by women living independently.

Vitamin supplementation and physical exercise performance

Vitamins, just as minerals and trace elements, meet with great interest in the world of sports because of their supposed role in enhancing physical performance. Of the 13 compounds now considered as vitamins, most water-soluble vitamins and vitamin E are involved in mitochondrial energy metabolism. The influence of vitamin supplementation on mitochondrial metabolism is largely unknown. The principal argument for vitamin supplementation is the assumed increased vitamin requirement of athletes. Theoretically, an increased requirement can be caused by decreased absorption by the gastrointestinal tract, increased excretion in sweat, urine and faeces, increased turnover, as well as biochemical adaptation to training. Of course, a marginal low vitamin status can simply be the consequence of a long-term inadequate intake. However, considering the RDAs there are no indications that long-term vitamin intake among athletes is insufficient. Neither are there indications that vitamin excretion or turnover is increased in athletes. However, it is very likely that the (apparently) increased requirement is the consequence of biochemical adaptation to training and does not indicate a decreased intake. Although a marginal vitamin status, induced by inadequate vitamin intake, may have a negative effect on performance, there is no evidence to support the view that this occurs in trained athletes. Moreover, vitamin supplementation in athletes with an adequate vitamin status has no effect on physical working capacity. Possibly, exceptions have to be made for the use of vitamin E at high altitudes and for the use of vitamin C and multiple B-vitamin supplements in hot climates.