Eating fructose（果糖） over an extended period of time does not lead to an increase in blood pressure, according to researchers at St. Michael's Hospital. A new study has found that despite previous research showing blood pressure rose in humans immediately after they consumed fructose, there is no evidence fructose increases blood pressure when it has been eaten for more than seven days.

In fact, researchers led by Drs. David Jenkins and John Sievenpiper observed a significant decrease in diastolic blood pressure -- the measure of blood pressure when the heart is relaxed between contractions- in people who had eaten fructose for an extended period of time.

"A lot of health concerns have been raised about fructose being a dietary risk factor for hypertension, which can lead to stroke, cardiovascular disease, renal（肾的） disease and death," said Vanessa Ha, a Master of Nutritional Sciences student and the lead author of the paper. "However, we wanted to determine whether fructose itself raised blood pressure, or if the apparent harm attributed to fructose was simply because people are eating too many calories."

For example, we know that people are consuming more soft drinks than ever, but is it the fructose, the extra calories, or possible other factors that are adding to their illnesses, she said.

The study looked at the effect of all sources of fructose, including natural and crystalline. Fruits are the primary source of naturally occurring fructose, and the fructose molecule found in fruits and vegetables is the same fructose found in high-fructose corn syrup（糖浆） . Crystalline fructose is a processed form which has added water and trace minerals.

In the systematic review and meta-analysis, Ha and colleagues pooled the results of 13 controlled feeding trials which investigated the effects of fructose on blood pressure in people who had ingested fructose for more than seven days.

The 352 participants included in their analysis ate an average of 78.5g of fructose every day for about four weeks. The U.S. average is an estimated 49g per day.

The paper is published in a recent edition of Hypertension, a journal of the American Heart Association.