The findings are based on an examination of 2006 data on 1.8 million donations from people of all ages from nine U.S. regions.

Dr. Anne F. Eder of the American Red Cross in Washington, the lead author of the study, and colleagues found that complications such as lightheadedness, loss of consciousness or bruising occurred in nearly 10.7 percent of donations by 16- and 17-year olds, 8.3 percent of donations by 18- and 19-year olds and only in 2.8 percent of donations by people age 20 and up.

Also, injuries related to fainting such as laceration requiring stitches, concussion, dental injuries and broken jaws, were more than twice as frequent in 16- and 17-year olds compared to 18- and 19-year olds and more than 14.56 times as likely than in the over-20 group.

These negative events can interfere with the willingness do donate blood again of this category of donors. The study found that only 52 percent of 16-year-olds who experienced a problem, no matter how serious or not it was, returned for a repeat donation within a year, compared to 73 percent of those who had no event.

“Consequently, any negative experience diminishes the likelihood of return blood donation, and increases the possibility that a short-term yield in donations incurs the ultimate expense of deterring future blood donation by young donors,” the researchers wrote.

The study found that even a minor complication such as sweating, becoming pale or feeling lightheaded without loss of consciousness, decreased donors’ willingness to return and donate blood within a year by 60 percent compared with those who did not experience donation-related problems.

Another surprising finding of the study was how many young donors are involved in blood donation. Dr. Eder explained this finding saying there is an increased demand for blood and limited supply of eligible donors. Only an estimated 38 percent of the U.S. adult population is currently eligible to donate blood due to factors including increased restrictions such as screening for West Nile virus and Chagas disease.

Therefore, blood centers recruit more blood donors by advocating states to accept blood donated by 16- and 17-year old high school students. At the same time, the rate of donations from older individuals has declined. This increased might be also explained by the fact that most states allow donation by 17-year-olds without parental consent. Only 22 U.S. states allow donation by 16-year-olds with parental consent and just 2 allow donation by 16-year-olds without parental consent.

“These findings are particularly pertinent at a time when blood centers are becoming increasingly reliant on young donors to maintain an adequate blood supply,” was the researchers’ conclusion.

They also recommended donors drink lots of water, get a good night’s sleep and eat a nutritious meal before donating blood in order to avoid donation-related problems.

The findings of the study, called “Adverse Reactions to Allogeneic Whole Blood Donation by 16- and 17-Year-Olds,” were published in the May 21 issue of the Journal of the American Medical Association.