Water-soluble vitamins

Vitamin B6

There are three main forms of vitamin B6: pyridoxine, pyridoxal, and pyridoxamine. The active forms of the coenzyme vitamin B6 are pyridoxal 5-phosphate and pyridoxamine 5-phosphate. Vitamin B6 is involved in about 100 metabolic reactions, including gluconeogenesis, niacin synthesis, and lipid metabolism.

Optimal intake of vitamin B6

Dietary Reference Intakes, Adequate Intakes, and/or Recommended Dietary Allowances (RDAs) for vitamins and minerals, including vitamin B6, are issued by the Food and Nutrition Board, Institute of Medicine, National Academy of Sciences. The most current RDAs for vitamin B6 are included in the Appendix. Tables of Adequate Intakes, Recommended Dietary Allowances (RDAs), and Estimated Average Requirements (EARs) and Tolerable Upper Intake (TELs) are included under the general heading of Dietary Reference Intakes (DRIs). Recommended Dietary Allowances (RDAs) are dietary intake levels that are adequate for approximately 98% of healthy individuals. Adequate Intakes (ARIs) are recommendations derived from observed or experimental data on nutrient intakes in a group (or groups) of healthy individuals and are used when RDAs cannot be determined. Estimated Average Requirements (EARs) are approximations of the nutrient requirements of half the healthy individuals in the group. Tolerable Upper Intake (TELs) are the largest amounts of a nutrient that most people can consume without adverse effects.

Recommendations for physically active people

Some studies suggest that exercise affects vitamin B6 metabolism, and that vitamin B6 deficiency impairs these parameters. Chronic exercise probably results in variable changes in vitamin B6 status, and its intensity may be related to vitamin B6 status. However, no differences in plasma vitamin B6 concentrations were observed with different intensities of bicycle ergometry. The variable effects of exercise on changes in plasma vitamin B6 status make it difficult to determine whether physically active individuals require more vitamin B6 in their diet than sedentary individuals. To investigate this issue, 22 physically active men were given either high doses of vitamin and mineral supplements or placebo.

Blood B vitamin levels increased significantly but decreased when supplementation was stopped. Blood vitamin A, vitamin C, zinc, magnesium, and calcium levels did not change, suggesting that physically active individuals may have increased B vitamin requirements. The effects of supplementation on these levels were not considered. However, these studies suggest that physically active individuals do not require high doses of vitamin B6, but that deficiency requires supplementation to the dietary reference intake (DRI) level or higher. Because the data on the relationship between vitamin B6 and exercise are limited, further study is needed before more definitive B6 recommendations can be made for physically active individuals.

Vitamin B12 and phthalate

Vitamin B12, or cyanocobalamin, and folate (folic acid) are essential for DNA synthesis and are interrelated in metabolism. They are essential for normal red blood cell synthesis, and it is through this function that these vitamins can influence physical activity.

Recommendations for physically active individuals

Inadequate intake of vitamin B12 and folate may be a cause of megaloblastic anemia. Because vitamin B12 is slowly excreted in bile and then reabsorbed, it takes about 20 years for healthy individuals to develop signs of deficiency. However, vitamin B12 supplements are recommended for vegetarian athletes. Adequate intake of vitamin B12 is a matter of particular concern for vegetarians, since it is found exclusively in animal products. In addition, athletes take vitamin and mineral supplements with megadoses (500-1000 mg) of vitamin C, which may reduce the bioavailability of dietary vitamin B12 and lead to deficiency. Athletes whose diets contain sufficient amounts of vitamin B12 and folate may not suffer from their deficiency. For example, 82 men and women involved in various sports were given vitamin and mineral supplements or a placebo for 78 months. All athletes were on a diet that met the recommended daily intake of vitamins and minerals. Although vitamin and mineral supplementation did not improve any of the measured sport-specific parameters, Telford et al. did find an improvement in jumping ability and an increase in body mass in female basketball players. They hypothesized that most of the increase was due to an increase in fat mass and less to an increase in muscle mass, as the players' jumping ability improved. Of course, the benefits of supplementation and adequate vitamin and mineral intake have not been well studied. However, vitamin B12 and folate deficiencies can lead to increased serum homocysteine levels, which may contribute to cardiovascular disease. This suggests that physically active individuals should be concerned not only with their diet but also with their overall health.

Thiamine

Thiamine is involved in reactions that produce energy, partly as thiamine diphosphate (also known as thiamine pyrophosphate), in the citric acid cycle, branched-chain amino acid catabolism, and the pentose phosphate cycle. Thiamine is required for the conversion of pyruvate to acetyl CoA in carbohydrate oxidation. This conversion is essential for aerobic glucose oxidation, and its absence impairs athletic performance and health. Therefore, athletes need to consume adequate amounts of thiamine and carbohydrates.

Recommendations for physically active individuals

There appears to be a strong correlation between high-carbohydrate diets, physical activity, and thiamine requirements. This is a concern for athletes, as they require large amounts of carbohydrates in their diets. However, some researchers have noted that physically active individuals require more thiamine than sedentary individuals, so it would be prudent to recommend that athletes receive at least standard doses of thiamine to avoid thiamine depletion. Some literature suggests that thiamine doses up to twice the recommended dietary allowance (RDA) are safe and will meet the needs of physically active individuals. A multivitamin/mineral supplement given for 3 months failed to significantly increase serum thiamine levels in athletes, but these researchers did not measure any parameters after supplementation. Further research is needed to clearly determine whether thiamine requirements are higher in active individuals who train several times a day compared to those who train more moderately.

Riboflavin

Riboflavin is involved in a number of key metabolic reactions that are important during exercise: glycolysis, the citric acid cycle, and the electron transport chain. It is a precursor for the synthesis of the flavin coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which participate in oxidation-reduction reactions, acting as 1- and 2-electron carriers.

Recommendations for physically active individuals

Riboflavin levels may change in individuals who begin to exercise. However, physically active individuals who consume adequate amounts of riboflavin in their diet are not at risk of deficiency and should not exceed dietary standards. The effects of vitamin and mineral supplementation were studied in 30 athletes over a 3-month period. No significant increases in blood vitamin and mineral levels were observed. The exceptions were pyridoxine and riboflavin. Weight et al. concluded that these supplements are not necessary for individuals who exercise if their dietary intake of vitamins and minerals is adequate. However, the longer-term effects of exercise on riboflavin levels need to be studied and evaluated.

Niacin

Niacin, nicotinic acid, or nicotinamide. The coenzyme forms of nicotinamide are nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). Both are involved in glycolysis, the pentose cycle, the citric acid cycle, lipid synthesis, and the electron transport chain.

Recommendations for physically active individuals

Nicotinic acid is often used in pharmacological doses to lower serum cholesterol. It is possible that pharmacological doses of niacin may increase the utilization of carbohydrate as a substrate during exercise, while decreasing the availability of free amino acids. Despite this association with exercise, there is no reliable evidence to support the need for increased niacin supplementation in physically active individuals.

Given niacin's role in vasodilation, several researchers have studied the effects of niacin supplementation on thermoregulation with mixed results. However, it is important for exercisers to consume niacin at a level consistent with dietary standards to prevent energy utilization that may impair performance.

Sources of Niacin

Food sources of pantothenic acid include sunflower seeds, mushrooms, peanuts, brewer's yeast and broccoli.

Pantothenic acid

The biologically active forms of pantothenic acid are coenzyme A (CoA) and acyl transfer protein. Pantothenic acid is involved in the transfer of acyl groups. Pantothenic acid coenzymes are also involved in lipid synthesis, oxidation of pyruvate and alpha-ketoglutarate. Acetyl CoA is an important intermediate in the metabolism of fats, carbohydrates and proteins.

Recommendations for physically active individuals

The effects of pantothenic acid supplementation on exercise performance have not been well studied. For example, Nice et al. gave 18 trained men either pantothenic acid supplements (one group) or placebo (the other group) for 2 weeks. In a run to exhaustion test, there were no significant differences between the groups in time, heart rate, or blood biochemistry. Studies in trained pantothenate-deficient mice showed reduced body weight, liver and muscle glycogen content, and reduced run to exhaustion time compared to trained mice given pantothenate supplements. However, these results are difficult to extrapolate to humans. Research suggests that increased pantothenic acid intake provides no benefit to physically active individuals if their pantothenic acid status is adequate.

Biotin

Biotin is an essential cofactor for mitochondrial carboxylases (one carboxylase in the mitochondria and one in the cytosol). These carboxylase-dependent reactions are involved in energy metabolism, so biotin deficiency can potentially lead to poor performance.

Recommendations for physically active individuals

To date, the effects of biotin on exercise performance and biotin requirements in physically active individuals have not been studied.

[ 1 ], [ 2 ], [ 3 ], [ 4 ]

Sources of Biotin

Good food sources of biotin include peanut butter, hard-boiled eggs, sprouted wheat, egg noodles, Swiss cheese, and cauliflower. Biotin is thought to be synthesized by bacteria in the gastrointestinal tract of mammals, but there are no published studies on this topic.

Vitamin C

Vitamin C, ascorbic acid, ascorbate, or ascorbate monoanion is used to prevent colds. Although vitamin C supplements do not prevent colds, some studies show that they significantly reduce their severity and shorten the course of the disease. However, megadoses of one vitamin and/or mineral can impair the function of other vitamins and minerals. Vitamin C is involved in maintaining collagen synthesis, fatty acid oxidation, and neurotransmitter formation, and is an antioxidant.

Optimal consumption

There are no new RDAs, standards, or adequate levels for vitamin C, so the 1989 RDAs apply to this vitamin. These levels are subject to change by the Food and Nutrition Board of the Institute of Medicine of the National Academy of Sciences.

Recommendations for physically active individuals

Animal studies have shown that exercise reduces vitamin C levels in various tissues. Some studies suggest an ergogenic effect of vitamin C supplements on performance, while others have found no effect. It is likely that supplements do not improve exercise performance if adequate vitamin C is consumed. However, individuals who train may need to consume up to 100 mg of vitamin C per day to maintain adequate vitamin C levels and protect against exercise-induced oxidative damage. Ultra-endurance athletes may need to consume 500 mg or more of vitamin C per day. Peter et al. studied the effects of 600 mg of vitamin C per day versus placebo on upper respiratory tract infections in ultramarathon athletes. The researchers found that marathon runners who took vitamin C had significantly fewer infections than those who took placebo. Some researchers have found vitamin C levels in athletes below normal levels, while others have reported normal levels. Therefore, caution should be exercised when using blood vitamin C levels as surrogates in studies.

[ 5 ], [ 6 ], [ 7 ]

Choline

Choline (vitamin B4) is a vitamin-like compound that participates in the synthesis of the characteristic components of all cell membranes: phosphatidylcholine, lysophosphatidylcholine, cholineplasmogen and sphingomyelin, as well as methionine, carnitine and very low-density lipoprotein cholesterol. There is no information about obvious choline deficiency in humans.

Optimal consumption

Prior to the 1998 Dietary Guidelines, there were no choline intake standards. The appendix contains the most current standards for choline.

Recommendations for physically active individuals

Because choline is a precursor to acetylcholine and phosphatidylcholine, it is thought to be involved in nerve impulse transmission, strength enhancement, and obesity prevention. There is evidence that plasma choline levels are significantly reduced after long-distance swimming, running, and triathlon. However, not all studies have observed such a reduction. Only long-distance running and endurance exercise have shown a reduction in plasma choline levels. Furthermore, there is no evidence that choline supplementation improves performance or increases or decreases body fat.

Sources of Choline

Beef liver, peanut butter, lettuce, cauliflower, and wheat bread are the richest sources of choline (ranging from 5831 mmol-kg for beef liver to 968 mmol-kg for wheat bread). Potatoes, grape juice, tomatoes, bananas, and cucumbers are also good sources of choline.