Results from a double-blind, placebo-controlled study showed no significant difference in the heart rate and diastolic blood pressure of 18 young, healthy volunteers.
Bitter orange (citrus aurantium) is also known as synephrine. It is marketed as a traditional Chinese herbal medicine that could promote weight-loss. However, previous research has been conflicting.
The new study, reported in the journal Pharmacotherapy (Dec. 2005, Vol. 25, Issue 12, pp. 1719-1724), gave subjects either a placebo or a bitter orange dried fruit extract (450 mg standardized to 27 mg of synephrine). Blood pressure and heart rates were recorded after 1, 3, 5 and 8 hours after dosing.
"Bitter orange dried-fruit extract did not significantly alter the [heart rate] or blood pressure after a single dose was administered," wrote the researchers from the University of Conneticut.
Blood pressure for the placebo group was 115 mm Hg, while the extract sample group's average was 114 mm Hg.
The study focused on only a small sample population and used only one dose of synephrine. Significant further study is needed to ensure the safety of bitter orange with multiple doses.
Bitter orange has been the focus of considerable debate. A previous study from the University of California, San Francisco, claimed that commercially available bitter orange extracts, Advantra Z and Xenadrine EFX, caused an 18 per cent increase heart rate.
The maker of Advantra Z, Nutratech, hit back by saying that the heart rate increases were due to natural digestion following meals.
Nutratech claims that Advantra Z works by increasing the metabolic rate, the breakdown of fat, and the uptake of protein into the muscle, without increasing the heart rate or blood pressure.
Arnold Schwarzeneggar recently blacklisted bitter orange supplements for young athletes in California. Bill SB-37 demands that all high school athletes pledge not to use bitter orange supplements, as well as ephedra and DHEA. It also forbids the marketing of these supplements at high school sporting events.