CYCLING PERFORMANCE TIPS
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 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, megadoses pose a definite risk. Aside from the use of a general multivitamin once a day, leave vitamin A out of your training regimen.
The basis for many of the following comments on the potential benefits of Vitamin D supplementation for athletes is "Effects of Vitamin D on Skeletal Muscle and Athletic Performance" published in J Am Acad Orthop Surg. 2018 Apr 15;26(8):278-285 pubmed abstract.
Although Vitamin D has traditionally been associated with calcium homeostasis and bone metabolism, we knew that there were also Vitamin D receptors on muscle cells. As our understanding of vitamin D metabolism has grown, we now find that vitamin plays a significant role in muscle function, strength, and muscle recovery from injury as well.
The active form of Vitamin D is produced from the sunlight (UV) conversion of precursors from both plant sources (vitamin D2) and animal sources (vitamin D3). Although this conversion occurs with fairly minimal amounts of sun exposure, the increasing use of sunscreens and other skin covering strategies to diminish the risk of skin cancer has led to a significant increase in the number of marginally Vitamin D deficient individuals in the "normal" populations used to develop the normal Vitamin D reference levels for lab tests.
As a result many athletes who have in the past been labeled as "low normal" are actually within the Endocrine Society's insufficient range and most likely are not getting sufficient vitamin D to realize full bone and muscle benefits. The Endocrine Society's clinical practice guideline for the evaluation, prevention, and treatment of vitamin D deficiency define "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).
A systematic review of vitamin D status in >2,000 athletes with a mean age of 22 years found that 56% had vitamin D levles < 32 ng/mL) and thus were probably below the levels needed for maximum benefit. Then we have the yearly variation. Most winter sports and training occur indoors which means the athlete has the potential for adequate sun exposure for Vitamin D conversion in the summer months alone.
Vitamin D deficiency is real, more common in the winter (especially in higher latitudes), and still a risk in the summer when sunscreen is used (sunscreen cuts skin vitamin D production by 95%).
Using the revised range for blood vitamin D levels and re-analyzing the many clinical studies of athletic performance, it is clear that many of the benefits were due to the fact that the study group contained a significant number of deficient individuals.
What were the benefits of adequte Vitamin D?
How do I rate Vitamin D?
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.
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."