Plant material that is high in antioxidants shows the ability to have beneficial effects of mood disorders such as anxiety and depression. Citrus fruit is high in a number of phytochemical antioxidants particularly vitamin C and a number of polyphenols mainly belonging to the flavonoid family. Many different types of citrus fruit appear to share this ability to effectively treat mood disorders. A number of studies have looked at the beneficial effects of citrus fruit of mood disorders. For example, in one study, researchers investigated the mood elevating effects of essential oils from Citrus reticulata (mandarin orange) and Citrus latifolia (seedless lime) on the mood of mice exposed to stress. The essential oils from both plants significantly increased the sleep time of the animals suggesting that the essential oils had a sedative effect. Citrus reticulata was effective at decreasing generalised anxiety behaviour in the mice, but both essential oils were effective at reducing the obsessive compulsive behaviour of the mice.
Evidence suggests that citrus fruit can affect mental function. For example, it has been shown that bergamot orange (Citrus bergamia, pictured) is able to increase brain levels of GABA in the hippocampus of rats. Further, it is known that citrus extracts can lower corticosterone levels in animals. As disruption to the GABA system and stress may be major contributory factors in the development of mood disorders, this may partly explain their beneficial effects.
In another study, researchers investigated the effects of Citrus paradisi (grapefruit) on the mood of mice exposed to stress. Extracts of the leaves of the grapefruit plant were administered to the mice and the mice were exposed to laboratory tests designed to cause stress. The administration of extracts of the grapefruit leaves were effective at decreasing both the anxious and depressive behaviour exhibited by mice under these stressful conditions. In a further study, Citrus aurantium (bitter orange) was as effective at reducing preoperative anxiety in a group of human subjects. The effect of the bitter orange in this study was no different from that of the anti-anxiety medication diazepam. In another study, administration of Citrus bergamia (bergamot orange) oil by inhalation significantly reduced the anxious behaviour of rats exposed to experimental stress. The authors provided evidence that these effects were accompanied by a reduction in the corticosterone (stress hormone) release by the rats.
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