Can Cyclists Benefit from Vitamin Supplements?


By Katherine A. Beals, PhD, RD, FACSM, CSSD

The word, vitamin comes from vita, which is Latin for “life” and amine because when vitamins were first discovered they were thought to contain an amine (i.e., nitrogen-containing) group. The “e” was later dropped when scientists learned of the true nature of the substances. There is no doubt that adequate amounts of vitamins are necessary for health and optimal athletic performance. But, will supplementing with “excess” (i.e., more than the Recommended Dietary Allowance (RDA)) enhance performance? This month’s nutrition article describes the roles of vitamins in athletic performance and attempts to answer the question of whether cyclists will benefit from vitamin supplementation.

B Vitamins and Energy Metabolism

The B vitamins, including thiamin, riboflavin, niacin, vitamin B6, pantothenic acid and biotin function as co-enzymes for a variety of enzymes that catalyze reactions in energy metabolism. In other words they are needed to ensure that the enzymes driving the metabolic processes converting the foods we consume into the fuel your muscles use occur effectively and efficiently. It has been hypothesized that athletes might require higher amounts of these B vitamins than their sedentary counterparts because they are using those metabolic processes more due to their higher levels of physical activity. While research does show that a deficiency of the B vitamins can impair athletic performance, it has failed to show any benefit of supplementing with additional amounts (over and above the RDA). Moreover, some B vitamins, such as B6 and niacin can be toxic at high doses. Acute intakes of excess niacin can cause flushing and tingling in the extremities while chronically high intakes have been associated with liver damage. Similarly, large doses of vitamin B6 can cause irreversible peripheral neuropathy (i.e., damage to the peripheral nerves). Athletes can easily meet their B vitamin requirements by consuming a well-balanced diet that includes whole grains, dark green vegetables, dairy products, nuts, beans and meats.

B Vitamins and Red Blood Cell Formation

The B vitamins folate and vitamin B12 are required for a number of enzymes that are critical for DNA synthesis and amino acid metabolism. In addition, their role in assisting with cell division makes folate and vitamin B12 critical for growth, the synthesis of new cells, such as red blood cells, and for the repair of damaged cells and tissues. Based on these functions it is easy to see why cyclists might believe they could benefit with supplementing with these vitamins. However, not unlike research regarding the other B vitamins, while a deficiency of folate and vitamin B12 will likely impair athletic performance, supplementing with excess amounts of these vitamins will not improve performance. To ensure an adequate intake of folate, cyclists should consume a diet that is rich in leafy green vegetables, fortified cereals and grains, nuts and legumes. Vitamin B12 is found naturally only in animal products (e.g., meats, fish, poultry, shellfish, eggs and diary products); thus an athlete following a vegan diet needs to include fortified foods containing B12. Fortunately, most vegetarian food products are now fortified with vitamin B12, so inadequate intake are rarely a problem.

Antioxidant Vitamins (vitamins C and E)

Oxidative stress is associated with muscle damage and impaired muscle function and occurs when the generation of reactive oxygen and nitrogen species (RONS) exceeds the body’s inherent antioxidant defenses. Research suggests that vigorous endurance exercise causes significant increases in RONS that could potentially exceed the body’s antioxidant capacity. Thus, it has been suggested that supplementing with dietary antioxidants such as vitamins C and E may attenuate the oxidative stress caused by training and speed recovery from intense and/or exhaustive exercise.

While good in theory, the research has not supported the concept in practice. Antioxidant supplementation has been shown in some studies (but not others) to decrease the oxidative stress associated with intense training; however, it does not seem to translate into improvements in athletic performance. In fact, recent research indicates that supplementing with antioxidants may actually impede training adaptations and ultimately have a negative effect on performance. It appears as though RONS produced during exercise may actually aid in muscle cell adaptations to exercise and, thus, are an essential component of the overall training stimulus. High doses of antioxidants may prevent these beneficial adaptations from occurring. Thus, it is recommended that endurance athletes skip the antioxidant supplements and instead focus consuming a well-balanced diet rich in fruits and vegetables, which are natural sources of a variety of antioxidant substances.

Vitamin D- the “sunshine vitamin”

Historically, calcium has received most of the attention when it comes to nutrients supporting bone health. However, accumulating evidence suggests that vitamin D is as important if not more important for optimal bone strength. In addition to bone health, vitamin D plays a key role in the regulation of the growth and maintenance of the nervous system and skeletal muscle, immune function, and inflammatory regulation. Vitamin D is unique as a vitamin because humans can synthesize it given adequate UVB (i.e., sun) exposure. Nonetheless, research suggests that many athletes do not meet the current recommendation for vitamin D. This is especially true for athletes who may have insufficient UVB exposure because they live at northern latitudes, train mostly indoors or during “non-peak hours” (i.e., early in the morning or late in the afternoon/evening), have dark skin pigmentation, or regularly use sunscreen (an SPF of 15 reduces vitamin D synthesis by 95%!). For most cyclists, particularly those training in Utah, getting adequate sun exposure and, thus, synthesizing enough vitamin D is generally not a problem. But, if you are concerned about your vitamin D status, a simple blood test (offered by most physicians) will set your mind at ease. Because vitamin D is found naturally in a limited number of foods (e.g., fatty fish, egg yolks, and fortified dairy products), athletes with poor status will likely need to supplement. Your physician will put you on the appropriate supplementation regimen. Vitamin D does have an upper tolerable level (UL) of 4000 IU (100 micrograms per day), so it is not a good idea to supplement without knowing first if you are deficient.

The Bottom Line

As their name implies, vitamins are essential for life, health and optimal athletic performance and athletes would be well advised to make sure they are getting adequate amounts (i.e., the RDA) of them in their diets. However, research indicates that supplementing with excessive amounts (i.e., more than the RDA) is not beneficial and may actually be harmful to health and athletic performance. While it may sound a bit like a broken record, the fact remains, the optimal performance diet is one that contains a variety of fruits, vegetables, whole grains, beans, lean meats and diary or dairy alternatives.

Katherine Beals, PhD, RD, FACSM, CSSD. Is an Associate Professor in the Division of Nutrition at the University of Utah where she specializes in sport nutrition. She is a Fellow of the American College of Sports Medicine and a Certified Specialist in Sports Dietetics.

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