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CYCLING PERFORMANCE TIPS

  Last updated: 11/19/2018

VITAMINS AND MINERALS


Vitamin and mineral supplementation in the athlete

I have taken a daily multivitamin for years. And a B with C (often called stress tabs). Do they help? My rationale was that as long as they were not mega doses (which can be harmful with the fat soluble vitamins A and D) my only real risk was to my wallet. And it was insurance to cover me if my diet was lacking. I saw a recent on line article suggesting athletes could benefit from a list of vitamin and mineral supplements. So it got me thinking about what I do, and what the data might be. So the question on the table - "do you short change yourself if you don't use supplements (assuming a normal, well balanced diet)?"

Coenzyme Q-10 (COQ10)

Coenzyme Q-10 (ubiquinone or CoQ10) is not one of the traditional vitamins, but is often marketed in multi-vitamin preparations. It is fat-soluble and is found in particularly high levels in the mitochondria of muscles (which are the power houses of muscle activity). Which suggests that supplements might improve athletic performance.

Although athletes taking coenzyme Q-10 have higher blood levels of that enzyme, they do not improve their aerobic performance or endurance. To quote from Dr. Mirkin.com (where references are available), "...all studies showing that CoQ10 improves performance are weak, uncontrolled, supported by special interest groups, and/or have two few subjects to show improvement in performance. Of six placebo-controlled studies, one showed that cross country skiers raced faster after taking coenzyme Q-10 pills, but the other five showed no improvement in muscle energy metabolism, muscle fatigue, endurance, or maximal ability to take in and use oxygen (VO2 max)."

Vitamin A

Vitamin is best known for its role in night vision (why your mom told you to eat your carrots), and may play a role in preventing infections. It plays no role in energy metabolism or muscle function.

"Evidence of vitamin A and E deficiencies in athletic individuals is lacking apparently because body storage is appreciable.

"Studies on ...fat-soluble vitamin A deficiency have noted no decrease of endurance capacity."

Bottom line: There is no physiologic rational for vitamin A deficiency and poor performance, and actual clinical investigations have demonstrated no benefit of supplements. Even more important, as a fat soluble vitamin which can build up over time in fatty tissue, mega-doses pose a definite risk. Aside from the use of a general multivitamin once a day, leave vitamin A out of your training regimen.

Vitamin C

Vitamin C and vitamin E are the 2 major antioxidants in our diet. And their impacts on performance are similar. (for more detail see vitamin E below, which I happened to research and write first). Results are best summed up in a quote from what I felt was one of the best review articles:

This was supported by the findings and conclusion in another study: "Daily vitamin C and E supplementation attenuated increases in markers of mitochondrial biogenesis following endurance training. However .... there were no.....improvements in VO2 max and running performance. ....we advocate caution when considering antioxidant supplementation combined with endurance exercise."

Vitamin C deficiency (plasma vitamin C < 11 micromol/L) is less than 3% in the general population. And this is in those who do not eat citrus fruit (or drink fruit juice) regularly. And as to negative health effects? There may be an increase in the incidence of the number of common colds during the winter season in those who are marginally deficient, which could be blunted with a supplement of 1000 mg of vitamin C a day.

My take aways?

Vitamin D

My comments on Vitamin D supplements for athletes are based on these 3 articles.

Although Vitamin D usually comes up in discussions on strong bones, there are Vitamin D receptors on cells throughout the body (including muscle cells). And it now appears that it also plays a role in muscle function, muscle strength, and muscle recovery from injury.

The active form of Vitamin D is the result of sunlight (UV) conversion of precursors found in many of the foods we eat - vegetables (vitamin D2) and meat (vitamin D3). Although conversion happens with minimal amounts of sun exposure, the increasing use of sunscreens and other skin covering strategies to lower the risk of skin cancer has increased the risks of Vitamin D deficiency.

Add the normal decrease in vitamin d blood levels as the days shorten in winter, and deciding who might be vitamin d deficient becomes even more complicated.

The optimal blood levels of vitamin d is a topic of ongoing controversy. With increasing sunscreen use, the potential for more people to borderline deficient has increased. And in turn it is likely that more marginally Vitamin D deficient individuals are now included in the "normal" population used to set the Vitamin D blood level reference range.

This article is a nice summary of vitamin D metabolism and the current consensus on blood Vitamin D levels. The Endocrine Society defines "deficiency" as 25(OH)D levels < 20ng/mL (50 nmol/L), "insufficiency" as 25(OH)D levels of 21 to 29 ng/mL (50 to 75 nmol/L), and normal levels as >30 ng/mL (75 nmol/L). But as with all national societies, it is likely they are taking a conservative stand and normal is closer to the 50 - 90 ng/ml range.

Liberalizing what is considered normal is especially important for the athlete where a blood level of at least 40ng/ml (and up to 90) appears to improve neuromuscular function. As a result many athletes who have been told they are "low normal" may instead be insufficient when it comes to performance benefits.

Dr. Mirkin takes a the conservative position, blogging "most experts feel that any level above 20 ng/ml is normal... There is no evidence anywhere that people with hydroxy vitamin D levels above 30 are healthier than those between 20 and 30. If 'normal' blood levels of hydroxy vitamin D were set higher than 20 ng/ml, more than 80 percent of North Americans would be misdiagnosed as having low blood vitamin D levels."

He finishes his blog post with a reference to this study which suggests .... "vitamin D supplement benefits on 137 diseases do not support cause and effect, and are thus likely to be due to chance."

But it isn't that clear cut. And there are other studies, specific to athletes, that support a role for vitamin D supplements - especially when considered in light of a systematic review of vitamin D status in >2,000 athletes (mean age of 22) that found that 56% had vitamin D levels < 32 ng/mL. These are a couple conclusions:

But before you reach for that supplement bottle, it's important to stress that this is a fat soluble vitamin with definite toxicity risks. These are generally from hypercalcemia (a high blood calcium level) and include an array of symptoms, including anorexia, frequent urination, excessive thirst, nausea, vomiting, and in severe cases, altered mental status and kidney dysfunction.

What have I concluded?

  1. vitamin D levels above 40ng/ml are normal for an active individual
  2. vitamin D levels above 100 ng/ml are definitely abnormal - and calcium metabolism problems increases as the blood level increases.
  3. It is likely that blood levels below 50 ng/ml are insufficient for athletes and put them at risk for athletic injury and impaired strength performance.
  4. There are risks in the use of supplements without blood testing to provide guidance, especially with daily doses of Vit D3 > 2000 IU/day.
  5. Megadose therapy of vitamin D is dangerous.

What are your choices? As Dr. Mirkin points out, "Most people can get all the vitamin D that they need by exposing a few inches of skin to sunlight for a few minutes three times a week during the warmer months. And during winter months, it is safe to take 1000 IU/day of vitamin D." My reading of the literature suggest that you can safely take 2000 IU (a common pill dosage) a day with minimal risk. But beware that the old adage "if a little is good, a lot is better" does not apply to the fat soluble Vitamins such as vitamin D.

If you are concerned about your exact blood vitamin D levels, ask your physician for a blood test for hydroxy vitamin D (25(OH)D - the active form. Other vitamin D precursors are not a reliable indicator of your vitamin D status.

Vitamin E

Vitamin E is a natural anti-oxidant. Exercise, as well as various environmental toxins we encounter every day, result in the formation of unstable molecules called free radicals. Free radicals in turn "oxidize" and inactivate essential proteins and enzymes in the cell. Ant-oxidants are the group of compounds (including vitamin E) that minimize this damage. They are also referred to as "free-radical scavengers."

Vitamin E is found in foods with a high fat content - nuts, seeds, avocado, vegetable oils and wheat germ. Some dark leafy greens and fish are also good sources of vitamin E. There is a blood test which can identify vitamin E deficiency (alpha-tocopherol - normal level 5.5-17 mg/L. Unless you are on an extremely limited diet, or suffer from one of several medical conditions that can limit dietary fat absorption, vitamin E deficiency is rare.

Never the less, the antioxidant content of sports bars remains a major marketing slogan The argument? Physical exercise leads to the formation of excessive free radicals and thus requires more than just the amount of vitamin E (and C, another antioxidant) found in a normal diet.

But there is a flip side to that argument. It was suggested that free radicals stimulate reparative pathways in exercised muscles, and if those free radicals were eliminated, training adaptations might suffer. However even though daily vitamin E supplementation did dampen increases in the markers of mitochondrial development following endurance training, there is a lack of hard data (and here) that this negatively impacted training induced improvements in endurance performance.

How about training improvements on vitamin E supplements? In a study comparing maximal oxygen consumption, maximal power output, and workload at lactate threshold increased equally in both groups. And there were no differences between the two groups concerning any of the metabolic variables measured.

Finally, toxicity from overuse? The symptoms are quite varied, including nausea, diarrhea, stomach cramps, fatigue, weakness, headache, blurred vision, rash, and easy bruising and bleeding. And to top it off, there have been several reports of an association of prostate cancer with overuse and a recent meta analysis that suggested vitamin E supplements may actually increase all-cause mortality.

My take aways?

Iron

Iron is an essential component of many cellular enzymes as well as hemoglobin (the protein which is found in red blood cells and carries oxygen throughout the body). If you do not absorb enough iron (problems with the lining of the small intestine such as celiac disease, gastric weight loss surgery, a change in diet) or are losing blood (menstrual blood loss, intestinal bleeding), you can become iron deficient. And iron deficiency can occur before your blood count begins to fall. More on the physiology of iron balance as well as various diagnostic tests.

This has led to speculation that a low total body iron state without anemia may contribute to poor performance. In this scenario, the serum ferritin (a measure of body iron levels) would be low, but the blood count may not yet have started to drop. In addition, it has been suggested that these borderline low iron cases might be athletes with a ferritin at the low end of what is defined as the "normal" range.

There was a recent article that suggested that iron might be of benefit for those competing at altitude. But if you read the detail, it really is about iron helping the performance of anyone who is iron deficient. So unless you are iron deficient (have a low ferritin and low blood count), iron will not help your performance (at altitude or sea level), and if you have adequate total body iron stores, there are definite risks of iron overload and toxicity with unneeded supplements.

The final question - does increasing your iron intake - without a low blood iron/ferritin or anemia - provide a performance benefit. To quote from a review of the literature, "Iron supplementation can raise serum ferritin levels, but increases in ferritin concentration, unaccompanied by increases in hemoglobin concentration, have not been shown to increase endurance performance.

This series of articles is a good example of how these "myths" start - and then are perpetuated. First, the original article which, I feel, misrepresents the conclusions of the referenced study: Iron Levels and Altitude - taking supplements may increase the benefits of thin-air training. This article was then reprinted for cyclists in Bicycling: This Common Supplement Could Help You Ride Better at Altitude"

This was a pretty strong claim so I thought I'd look for more details in the original article in PLOS. Although the PLOS article was quoted as supporting improved athletic performance at altitude with iron supplements, as far as I can determine it only found that IRON DEFICIENT athletes incorporate more substrate (iron) into their blood cells if they were given supplements - which makes sense. They need iron (even at sea level as they are iron deficient), so given iron plus the stimulus of altitude, it is only reasonable to assume that they will absorb more of it. And as iron is in many enzymes (along with iron in blood cells), one might also expect some performance improvement (non heme level related) in the iron deficient athletes as well. And of course there is no evidence that the iron deficient group actually improved performance - only that the blood cell mass increased and thus it was assumed they would perform better as well.

So in my reading, this is a great example of an unfounded interpretation in the lay press that will lead to iron supplementation abuses by athletes who have adequate iron stores, and expose those looking for that performance edge to the toxicity of iron supplements.

Magnesium

Magnesium is involved in numerous cellular processes affecting muscle function including oxygen uptake, energy production and electrolyte balance. And has been identified as essential to over 600 enzymatic cellular processes. It would seem an ideal candidate to negatively impact athletic performance in deficient individuals, or to use as a supplement to improve athletic performance in those who might have only marginally normal total body magnesium stores. However, the data is sparse, and even those articles suggesting a significant magnesium deficiency rate in the general population, and a role in hypertension, preeclampsia, migraine, depression, coronary artery disease, and asthma fail to reference an impact on athletic performance.

In 2000 a review of the literature referenced only 12 studies on the use of magnesium supplements in athletes - no benefits. I could find just 1 that specifically studied the use of magnesium as a supplement in aerobic performance - a marathon, again no benefit. For those interested in more details, here is a nice review done in 2017 entitled "Can Magnesium Enhance Exercise Performance?"

One of the reasons we may see so little overt magnesium deficiency is the fact it is found in such a diversity of the foods we eat - green leafy vegetables, legumes, nuts, seeds, whole grains, fish, poultry, beef, and even chocolate. And our body can modify kidney loss and to protect total body stores as well. Metabolic unit depletion/repletion experiments show that serum magnesium concentrations decrease only after a prolonged depletion if an individual starts with an adequate magnesium status.

Magnesium is found in many foods but is especially concentrated in green-leaf vegetables, whole grains, white potatoes, nuts, and legumes. A blood level above 0.85 mmol/L (2.06 mg/dL) indicates normal total body stores. The Recommended Dietary Allowance is 250 mg/d, but as magnesium is so readily excreted in the kidneys, there are no significant side effects from the use of up to 960 mg/day as supplements.

My take always?

Zinc

There is no data that zinc is beneficial in exercise performance, and several studies that indicate it is harmful at higher doses. This article by Dr. Mirkin is a nice summary.

Zinc supplements are most commonly taken for their reported benefit to improve sexuality and sexual function. Zinc is concentrated in the prostate and the assumption was that "..if a little is good, more must be better." There is no evidence that zinc supplements have a positive effect on prostate infections, impotence, enlarged prostate or any other prostate disorders. And those taking zinc supplements have an increased rate of prostate cancer.

There is no study data to support a positive effect on athletic performance with the last data base search in 2012 failing to show any benefits for zinc supplementation. The conclusion of one of an earlier studies from 1994 is as valid today as it was then: "There is no conclusive evidence that supplementation with any of these trace minerals (including zinc) will enhance performance. A diet containing foods rich in micronutrients is recommended. However, for those athletes concerned that their diets may not be sufficient, a multivitamin/mineral supplement containing no more than the RDA may be advised."


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