Dietary Supplements And Exercise In The Heat
Chester J. Zelasko, Ph.D. | June 12, 2007

Summer is here and everyone is headed outside to exercise and work in the yard. Dehydration is always a concern, and that often raises questions about which supplements you should and shouldn’t take when working in the heat.

At the recent national convention of the American College of Sports Medicine, I attended an excellent session on using supplements in the heat such as creatine, glycerol, synephrine, and caffeine; this Newsletter is a summary of that research. In addition, there was a discussion about medications commonly used in children being treated with attention deficit hyperactivity disorder (ADHD) that’s important for parents.

Creatine is a dietary supplement used by athletes to increase muscle size; what actually happens is that creatine increases the fluid volume of muscle cells, making the muscle appear larger. One of the interesting characteristics of muscle is that if you increase the diameter of the muscle, even if it’s just with fluid, the muscle will be stronger. That allows an athlete to lift heavier weight--and that will actually build muscle.

One of the concerns about creatine is that it may contribute to dehydration if someone taking creatine as a supplement exercises in the heat. Several studies were presented that demonstrated that just the opposite is true, at least in trained athletes (1, 2). The creatine increased total body water and allowed the athletes to perform well in the heat.

There are two key points. First, the athletes had used the creatine for at least a week, which allowed fluid volumes to adapt. Second, these were trained athletes. Novices who take creatine because they hear it might be good for them may not get as positive an effect. The key is that whether you use creatine for exercise performance or whether you use it for fibromyalgia, muscular dystrophy, or any other muscle-wasting condition, drink an extra glass of water or two every day to keep body fluid at optimal levels.

Glycerol is a three-carbon molecule that the body can use for energy, the back-bone of triglycerides, and many other functions. When taken as a supplement, it increases fluid volume--in effect, it allows athletes to hyper-hydrate. I’ve used glycerol in the weeks before a marathon to increase fluid levels and delay dehydration. Again, research shows that glycerol is safe for athletes who exercise in the heat. What is less clear is whether it will improve performance.

Before you try glycerol, understand one thing. It can cause some serious digestive stress including loose stool that borders on diarrhea. This is not a supplement you use just once. You have to adapt to it, but it can keep you hydrated if used long term.

The February 2007 Newsletter summarizes the research presented. Caffeine presents no problem when used by athletes who work out in the heat. The interesting thing is that while caffeine may increase the need for urination, it does not change total body water. That’s why people have speculated it has a diuretic effect. That doesn’t seem to be the case when tested in athletes and in military personnel.

Synephrine (Bitter Orange)
When ephedra was banned a few years ago, a chemical cousin began appearing called synephrine. Synephrine is an extract from bitter orange (citrus aurantium). It seems to have similar properties for stimulating the central nervous system and increasing metabolic rate. Whether it’s effective or not was not the subject of the talk.

Ephedra contributed to the deaths of several professional athletes, and that’s what led to it being banned. Although the ban has been rescinded in part recently, any of the amphetamine-like herbs are a concern for athletes of all ages. The problem is not that it causes dehydration--the problem is that it masks fatigue. That allows athletes to push past the normal time when they would stop a workout. Combined with dehydration, that becomes lethal for work in the heat. The consensus was that synephrine should follow the same path as its cousin and be banned.

Children with ADHD
The panel concluded with a word of caution for parents of children with ADHD. These children are often prescribed central-nervous-system stimulants such as Adderall and Ritalin to help them cope with the symptoms of ADHD, but the potential problem is the same as for ephedra. These children may push themselves beyond fatigue, and that can mask typical dehydration effects on the body. While there’s no research to demonstrate that this has been a problem, there’s no research on the topic, period.

If you have children who take medications for ADHD, be sure they stay well hydrated when exercising and playing sports in the heat. Until more research is available, it’s better to err on the side of caution and keep the fluids flowing into the children, even though they may not feel thirsty.

The Bottom Line
Exercise and work in the heat can be safe and may be helped with the proper use of the right nutrients. The key is starting slowly and going through an adaptation phase. That way, whether you drink coffee or want to try creatine, your total body water can adapt to the supplement before you venture out into the heat. Keep the fluids going and enjoy the summer.

  1. Weiss BA, Powers ME. Creatine supplementation does not impair the thermoregulatory response during a bout of exercise in the heat. J Sports Med Phys Fitness. 2006. 46(4):555-63.

  2. Easton C, et al. Creatine and glycerol hyperhydration in trained subjects before exercise in the heat. Int J Sport Nutr Exerc Metab. 2007. 17(1):70-91.
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