Though there have been many studies on caffeine-laden energy drinks, popular especially among the youth, a latest research which suggests that they might make blood vessels less efficient is cause for further alarm. These drinks have been linked to heart, nerve and stomach problems. Lead researcher Dr John Higgins, a professor of medicine at McGovern Medical School at the University of Texas Health Science Center in Houston, explains energy drinks that reduce the vessels’ diameter, in effect, restrict blood flow and oxygen delivery. 
This should be read in conjunction with the fact that many people use energy drinks when they exercise, a time when arterial function ought to be at its top. Exercise and sports require maximum blood flow so oxygen can get to cells quickly, Higgins said. When energy drinks are consumed its more work for the heart and less oxygen supply for the heart. This could explain why there have been cases where kids have had a cardiac arrest after an energy drink. “These drinks are not intended for children,” Higgins warned. In addition, people under 18, women who are pregnant or breastfeeding, caffeine-sensitive individuals, those taking stimulants or caffeine-based drugs or those with heart disease should stay away from energy drinks, he added.
The study included 44 healthy, non-smoking medical students in their 20s. The researchers tested the effect of a 24-ounce energy drink on cells lining blood vessels, called endothelial cells. The function of these cells was tested before and after the participants consumed the energy drink, and again 90 minutes later. The researchers looked at artery flow-mediated dilation – an ultrasound measurement that is an indicator of overall blood vessel health. After 90 minutes, the internal diameter of blood vessels tested was dramatically smaller, on average, than before, the investigators found.
This negative effect on blood vessels may be related to ingredients in the energy drink, such as caffeine, taurine, sugar and other herbals, the researchers suggested. Dr David Katz, director of Yale University’s Yale-Griffin Prevention Research Center, described the small study as one that looks only at acute effects and cannot be considered proof that energy drinks injure the cardiovascular system over time. However, the combination of sugar and stimulants in these drinks has no proven benefit, he added. “There are far better ways to boost energy, such as standing up and getting a bit of exercise,” he suggested. “In the absence of a reliable benefit, even a low level of risk is objectionable.”
A spokesman for an industry group that represents makers of energy drinks said the drinks are safe. “Mainstream energy drinks contain about half the caffeine of a similarly sized cup of coffeehouse coffee, and have been extensively studied and confirmed safe for consumption by government safety authorities worldwide,” said William Dermody, spokesman for the American Beverage Association. “Nothing in this preliminary research counters this well-established fact.” A meeting of the American Heart Association, in Chicago, was expected to discuss the study. Research presented at meetings is typically considered preliminary until published in a peer-reviewed journal.