Eating before donating blood may cause dizzies

The risk of blood donors suffering side effects such as dizziness is seven times higher when they donate blood shortly after a meal, according to an Osaka Red Cross Blood Center survey released Friday.

It was the first time a large-scale survey on blood donors revealed a relationship between the time of food intake and symptoms of vasovagal reflex, a side effect of changes in blood circulation and psychological tension that can occur after a blood donation.

Every year, tens of thousands of blood donors in Japan suffer from vasovagal reflex symptoms — which also include nausea, cramps and loss of consciousness — and there are many cases in which donors are injured as a result, according to the center.

“When we are full, blood accumulates near the abdomen for digestion. As a result, less blood flows to the brain, which is believed to make it easier for vasovagal reflex to occur,” said Yoshihiko Tani, deputy head of the Osaka Red Cross Blood Center.

The center surveyed 329,005 donors between last June and February on such things as meal times and sleeping hours. It found 1,055 of them suffered from vasovagal reflex symptoms during or after donating blood.

The rate of vasovagal reflex occurrence was highest among donors who had a meal within two hours of donating blood, at 0.85 percent. This was about seven times higher than the 0.12 percent among those who ate five to six hours prior to donating blood.

The rate for those who ate two to three hours ahead was 0.36 percent, three to four hours 0.35 percent, and eight hours or more 0.27 percent, according to the survey.

Other factors that may trigger the symptoms included being young, having a relatively low blood circulation level, and not having gotten used to donating blood.

Of the 5.8 million people who donated blood across Japan in fiscal 2002, 43,000 suffered vasovagal reflex symptoms.