Fat-soluble vitamins

Fat-soluble vitamins include vitamins A, D, E, and K. Data on fat-soluble vitamins other than vitamin E and their relationship to exercise are limited. Recent evidence suggests that excess vitamin A may cause decreased bone mineral density and increase the risk of hip fractures. It has been noted that megadoses of vitamin A also have harmful effects on the body.

Although vitamin A is well known as an antioxidant, beta-carotene is not an effective antioxidant and may be a pro-oxidant. Beta-carotene derivatives have been shown to be present in the lungs and arterial blood, possibly stimulating tumor growth, especially in smokers and those who inhale tobacco smoke and car exhaust. Therefore, people who exercise, especially those living in urban areas with lots of traffic, should not take beta-carotene supplements.

• Vitamin A

Vitamin A is a fat-soluble vitamin. It affects vision, participates in cell differentiation, reproductive processes, pregnancy, fetal development and bone tissue formation. RDA for vitamin A is given in the Appendix.

Recommendations for physically active individuals. Estimates of vitamin A intake in physically active individuals vary widely, but some are flawed because they do not specify the source of the vitamin (plant or animal). Individuals who consume few fruits and vegetables tend to have lower levels of vitamin A than those who eat a lot of fruits and vegetables. Because vitamin A is fat-soluble and accumulates in the body, mega doses are not recommended.

Vitamin A is also known as an antioxidant. For athletes, it can be ergogenic.

• Vitamin D

Vitamin D (calciferol) regulates calcium and phosphorus metabolism in the body. Its importance lies in maintaining calcium homeostasis and bone structure. Vitamin D is synthesized in the human body under the influence of sunlight from provitamin D3. The conversion of vitamin D into its more active forms begins first in the liver, then in the kidneys, where 1-alpha-hydroxylase adds a second hydroxyl group to the first position on 25-hydroxyvitamin D, resulting in 1,25-dihydroxyvitamin D3 (1,25 -(OH)2D3). The most active form of vitamin D is calcitriol. The effect of calcitriol on calcium metabolism is discussed in more detail in the Calcium section. The appendix contains vitamin D standards.

Recommendations for physically active individuals. To date, there has been little research on the effects of physical activity on vitamin D requirements and its effects on exercise performance. However, there is evidence that weightlifting may increase serum levels of calcitriol and Gla protein (an indicator of bone formation), resulting in improved bone healing. Bell et al. reported changes in serum calcitriol levels, but no changes in calcium, phosphate, or magnesium. Furthermore, there is compelling evidence for an effect of 1,25-dihydroxyvitamin on muscle function; 1,25-dihydroxyvitamin D3 receptors have been detected in cultured human muscle cells. However, daily supplementation of 0.50 μg 1,25-dihydroxyvitamin D3 for 6 months in 69-year-old men and women did not improve muscle strength. However, as with other nutrients, vitamin D status should be checked in athletes who consume a low-calorie diet because long-term adverse effects on calcium homeostasis and bone mineral density may occur. Furthermore, vitamin D requirements may be higher during the winter months in individuals living at latitudes of 42° or higher (e.g., New England states) to prevent increased parathyroid hormone secretion and decreased bone mineral density.

Sources: Few foods contain vitamin D. The best food sources are fortified milk, fatty fish, and fortified breakfast cereals. Spending 15 minutes in the sun each day also provides adequate vitamin D.

• Vitamin E

Vitamin E belongs to a family of eight related compounds known as tocopherols and tocotrienols. Like vitamin A, it is well known for its antioxidant activity, which prevents free radical damage to cell membranes. Vitamin E is also known to play a role in immune processes. Vitamin E requirements are based on the RDI and are listed in the Appendix.

Recommendations for physically active individuals. The effect of exercise on vitamin E requirements was assessed. Some scientists noted a significant relationship between lifelong physical activity and vitamin E levels in men living in Northern Ireland, others concluded that physical exercise causes a decrease in muscle vitamin E levels, which is restored after 24 hours or more, as well as a redistribution of vitamin E between the liver and muscles, and vice versa, while others claim that regular or one-time exercise does not affect vitamin E concentrations in individuals with different levels of fitness.

A series of studies were conducted to further evaluate the effects of exercise on vitamin E levels. Since endurance exercise increases oxygen consumption, thereby increasing oxidant tension, it seems logical that vitamin E supplementation would benefit physically active individuals. In addition, exercise increases body temperature, catecholamine levels, lactic acid production, and transient tissue hypoxia and reoxygenation, all of which contribute to free radical formation. Furthermore, one of the physiological responses to exercise is an increase in the size and number of mitochondria, which are the site of reactive oxygen species production. They also contain unsaturated lipids, iron, and unpaired electrons, making them key sites for free radical attack. Vitamin E protects skeletal muscle from free radical damage and may also have ergogenic effects.

Many studies have determined the effects of exercise, vitamin E levels, and supplements on oxidative damage to skeletal muscle and antioxidant enzyme activity. A number of animal studies suggest that vitamin E supplements reduce exercise-induced oxidative damage; only a few studies have been conducted in humans. Reddy et al. studied the effects of acute exhaustive exercise in rats and found that free radical production was greater in rats deficient in vitamin E and selenium than in rats supplemented with these vitamins. Vasankari et al. studied the effects of supplementation with 294 mg vitamin E, 1000 mg vitamin C, and 60 mg ubiquinone on endurance performance in eight male runners. They found that these supplements increased antioxidant capacity and that when vitamin E was added with other antioxidants, it had a synergistic effect in preventing LDL oxidation. Other studies have shown reduced serum creatine kinase, an indicator of muscle damage, in marathon runners who received vitamin E and C supplements. McBride et al. studied the effects of exercise training and vitamin E supplementation on free radical formation. Twelve resistance-trained men were given 1200 IU of vitamin E supplements (alpha-tocopherol succinate) or placebo for 2 weeks. Both groups showed increases in creatine kinase activity and malondialdehyde levels before and after exercise, but vitamin E reduced the increase in these values after exercise, thereby reducing muscle membrane damage. Additionally, vitamin E supplementation does not appear to be effective as an ergogenic aid. Although vitamin E reduces free radical formation in exercisers, reducing membrane rupture, there is no evidence that vitamin E actually increases these parameters. However, the role of vitamin E in preventing exercise-induced oxidative damage may be significant and further studies to determine this effect are needed.

• Vitamins of group K

The K vitamins are fat-soluble and heat-stable. Phylloquinone, or phytonadone (vitamin K), is found in plants; menaquinone (vitamin K2) is produced by bacteria in the intestines, satisfying the daily requirement for vitamin K; mepadione (vitamin K3) is a synthetic form of vitamin K.

Alkalis, strong acids, radiation and oxidizing agents can destroy vitamin K. The vitamin is absorbed from the upper surface of the small intestine with the help of bile or its salts, as well as pancreatic juice, and then transported to the liver for the synthesis of prothrombin, a key factor in blood clotting.

Vitamin K is necessary for normal blood clotting, for the synthesis of prothrombin and other proteins (factors IX, VII and X) involved in blood coagulation. Vitamin K, with the help of potassium and calcium, is involved in the conversion of prothrombin to thrombin. Thrombin is an important factor in the conversion of fibrinogen to an active fibrin clot. Coumarin acts as an anticoagulant, competing with vitamin K. Coumarin, or synthetic dicoumarin, is used in medicine primarily as an oral anticoagulant to reduce prothrombin levels. Salicylates, such as aspirin, which is often taken by patients who have had a myocardial infarction, increase the need for vitamin K. Vitamin K has been shown to affect bone metabolism by facilitating the synthesis of osteocalcin (also known as bone protein). Bone contains proteins with gamma-carboxyglutamate residues, which are dependent on vitamin K. Impaired vitamin K metabolism is due to inadequate carboxylation of the non-collagenous bone protein osteocalcin (containing gamma-carboxyglutamate residues). If osteocalcin is incompletely carboxylated, normal bone formation is impaired. Optimum Intake. The RDI for vitamin K is given in the Appendix. The average diet usually provides at least a minimum of 75-150 mcg/day of vitamin A and a maximum of 300-700 mcg/day. Absorption of vitamin K may vary among individuals but is estimated to be 20-60% of total intake. Toxicity from vitamin K in natural sources is rare and is more evident from synthetic sources of vitamin K used medicinally. Vitamin K deficiency is more common than previously thought. Western diets high in sugar and processed foods, megadoses of vitamins A and E, and antibiotics can contribute to decreased function of gut bacteria, leading to decreased production and/or breakdown of vitamin K.

Recommendations for physically active individuals. There are no studies on vitamin K in relation to exercise or ergogenic effects. Since vitamin K is not absorbed as efficiently as previously thought, its role in preventing bone loss has become more apparent and may provide impetus for research into the role of vitamin K in athletes, particularly women.

Sources: The best food sources of vitamin K are green leafy vegetables, liver, broccoli, peas, and green beans.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ]