a jest tych badań wiele chyba akurat witamina C jest najpopularniejsza w tej kwestii
w jednym sprawdzono wchłanialnosc wit C [askorbinian]
przy 1.5g dziennie jest to 50%
przy 16g dziennie tylko 16% wiec wieksza dawka niz 2-3g nie ma sensu
do 1.5g kwasu askorbinowego nie przeszkadza też nerkom
powyżej moze miec wplyw i w zwiazku z tym jest wydalana w wiekszej iosci - jak wyzej napisalem
+ odnosnie wplywu na trening
The evidence addressing the vitamin C requirement of athletes is abundant and contradictory. Multiple studies have found blood and plasma levels of vitamin C to be diminished in those who exercise. Keith (24) summarizes the findings of Namyslowski who published two papers addressing the requirement of ascorbate in exercising individuals. The second study concluded that blood vitamin C levels decreased in athletes ingesting
100 mg per day. A dietary intake of 300 mg/day maintained blood levels of the vitamin. This was some of the first evidence to suggest vitamin C needs are increased in those who exercise. Athletes receiving a one-gram vitamin C supplement showed increased work capacity at a heart rate of 170 beats per minute. Subjects served as self-controls and were given a placebo for two weeks and then vitamin C for two weeks. During vitamin C supplementation subjects repeatedly demonstrated decreased heart rates at all levels of work when compared with the placebo trial (16). However, treatments (placebo or vitamin) were given in succession. An alternate study by Telford et al. (35) provided evidence that supplementation for 7 to 8 months did not have any significant effect on blood levels of the vitamin. However, females were shown to have significantly higher levels of vitamin C in their blood versus the male population. Also, this study showed that plasma vitamin C levels could remain elevated for 24 hours after strenuous exercise (11,39). Vitamin C has shown favorable effects when used during heat acclimatization in humans. Two separate studies (26, 33) from the 1970s have both shown similar results. Plasma levels of ascorbic acid in thirteen male volunteers rose to a level fourfold higher in supplemented (250 mg or 500 mg) than unsupplemented subjects. The higher plasma levels of ascorbate were associated with reduced body temperature and sweat loss. These results support the hypothesis that vitamin C is beneficial to those trying to acclimatize themselves to heat (27). In a study done one year earlier the same results were found. However, it was determined that doses of 500 mg versus 250 mg result in no enhanced benefits in subjects acclimatizing to heat (33). The effects of vitamin C supplementation on anaerobic and aerobic work capacity were investigated by Keren and Epstein (26). Thirty-three healthy males partook in a 21-day training session that uses primarily involved mainly aerobic work. Measures of aerobic and anaerobic work capacity were then measured. Vitamin C supplementation provided no enhancement in either aerobic or anaerobic work. Many ultra long-distance runners experience upper respiratory tract infections. Peters et al. (30) addressed the possible role of vitamin C in preventing these infections. Symptoms of upper respiratory infection were monitored for 14 days after an ultramarathon (> 26.2 miles) in subjects receiving either placebo or vitamin C supplementation. Sixty-eight percent of the runners on the placebo reported the development of respiratory tract infections. In contrast only one-third of the vitamin C group reported the infections. The scientists concluded that vitamin C supplementation may actually be beneficial in helping prevent upper respiratory infections in ultramarathoners. Blood vitamin C levels greater than 0.6mg/100ml have been established as being adequate (41). Multiple studies have shown blood vitamin C levels of various athletes including runners (11,40) to be adequate. Concentrations of plasma AA have been reported to be significantly higher five minutes after a 21 km (13.1 mile) run than baseline values. The levels then fell 20% below pre-exercise values within 24 hours and remained depressed for 2 days (11). This may be due to a loss in plasma volume following exercise. Contradictory results were found by Rokitzki et al. (31) and Glesson et al. (11) who found that vitamin C was higher immediately after exercise. However, Rokitzki et al. (31) also noted that the levels remained high for 24 hours following a marathon. The fluctuating levels of vitamin C are likely controlled by the adrenal gland (11). In conclusion, a high probability exists that a large majority of athletes consume sufficient vitamin C in their diet. At the same time it is know that a diet lacking vitamin C will in turn inhibit performance (5). A daily intake between 100-300 mg of vitamin C may be warranted to meet the needs of all people who exercise (5). However, until an alternative RDI for athletes is established the recommended intake for vitamin C shall remain at 75 mg for women and 90 mg for men. Doses of 1500 milligrams or greater oversaturate the body pool and are excreted in the urine. Therefore, multiple large doses are not warranted. One must also be aware of the enzyme kinetics of vitamin C transport. Multiple small doses help prevent side effects and are advised for those choosing to consume large quantities or supplement with the vitamin. The previously mentioned levels are easily obtainable by substituting a well-balanced diet for a supplement. Clarkson summarizes (7) that athletes taking a multivitamin do not appear to obtain ergogenic benefits and likely do not need the supplementation (40). However, a small portion of those who exercise will lack an adequate vitamin C intake. Bazzarre et al. (3) have shown some bodybuilders have vitamin C intakes below 40 mg. Similar conclusions were found in basketball players (15), cyclists (25), and even Navy Seals (8). Currently it appears that the variety and adequacy of individual diets will determine if supplementation with vitamin C is needed
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