Ribose is a five-carbon simple sugar (a pentose) that forms the carbohydrate portion, or backbone, of RNA and DNA molecules. When combined with adenine, ribose produces adenosine, one of the components of the energy currency of the cell, ATP. Ribose is used in the body in several specific ways. It can be converted into pyruvate and enter into the pathways of energy metabolism, or it can be used to manufacture nucleotides, the primary building blocks for important structures in the body such as RNA, DNA, and ATP. As a result, ribose supplements are typically marketed for increasing energy levels, exercise endurance, and muscular power output.
Clearly, anybody concerned with managing diminished blood flow to the heart or muscle tissues would be interested in ribose supplementation. In particular, people who experience chest pain, shortness of breath, or leg pain during exercise may want to consider ribose as a daily dietary supplement.
The casual or occasional exerciser is unlikely to benefit from ribose supplements except in the case of several back-to-back days of intense exercise. For the “weekend warrior,” who probably has enough time between exercise sessions to fully recover ATP levels, supplemental ribose is not recommended. Competitive athletes, who may be training once or more per day, could notice very modest benefits such as increased power output and increased time to exhaustion with regular ribose supplementation (because of enhanced ATP resynthesis following exercise-induced depletion); required doses, however, are large (more than 10 g/day) and expensive.
Because ribose can serve as a precursor to adenosine (the A in ATP} and seems to stimulate the production of ATP (in laboratory studies), the theory behind ribose supplementation is that it maximizes ATP stores and therefore increases cellular energy stores for improved exercise performance and fatigue prevention.
In the cell, ATP loses its phosphate groups to generate energy. Losing one phosphate turns ATP (triphosphate) into ADP (diphosphate) and finally into AMP (monophosphate). Adenine or adenosine (no phosphates) can either be converted back to AMP or lost from the cell. The conversion back to AMP/ADP/ATP or the “salvage” of adenosine requires a ribose-containing molecule known as 5-phosphororibosyI-l-pyro-phosphate (PRPP). If this salvage does not take place, the adenosine is lost and must be converted “from scratch” a process known as de novo synthesis, which again requires the ribose-containing PRPP.
Ribose has been understudy as a therapy for cardiac ischemia (reduced blood flow to die heart) for a number of years (Pasque and Wechsler, 1984). The data from those studies clearly indicate that ribose can help improve heart function during and following periods of reduced blood flow and oxygen delivery (Erickson, 1990), Under conditions of constricted blood and oxygen flow to heart and muscle tissue, ATP levels have been shown to decrease by as much as 50%. This finding is not unexpected, but the fact that creatine phosphate levels recover relatively quickly while ATP levels may remain depressed for several days suggests that adenosine levels may not be adequately maintained. In animal studies, supplemental ribose permits recovery of approximately 85% of normal ATP levels within 24 hours following restricted circulation.
In patients with coronary artery disease, supplemental ribose allows subjects to exercise forsignificandy longer periods than they could before they consumed ribose and longer than subjects who consumed a placebo supplement (Pliml et al., 1992). During intense exercise, ATP levels are reduced 10-20%, which may be attributed to the loss of adenosine and inadequate resynthesis of ATP (Wagner et al., 1991). In some muscle fibers, complete resyndiesis of ATP may require 24-96 hours (1-4 days) to fully recover from exhaustive exercise. Supplemental ribose has the potential to increase the rate of adenosine production and ATP synthesis following exhaustive exercise by approximately 3-4 times, meaning that recovery of ATP stores can be reduced from 1-4 days to 6-24 hours (Wagner et al., 1991).
Because ribose is found in all cells of the body, it is generally recognized as a nontoxic substance. Supplemental doses of as much as 60 g/day have been given with no significant side effects (Erickson, 1990). At such high levels, die possible occurrence of gastrointestinal distress, diarrhea, and hypoglycemia are more likely. For purposes of maintaining elevated levels of ribose in the blood, smaller doses of 3-10 g/day of ribose are common in commercial dietary supplements, but as noted earlier, the clinical evidence for energy or endurance benefits of such doses in healthy subjects has been disappointing.