Newly published data in the American Journal of Clinical Nutrition indicated that different flavonoid classes conferred different risk reductions, with the highest intakes of flavonol, flavone, and flavanone associated with a significant 7–10% reduction in depression risk.
The associations were also observed for flavonoid-rich foods, with, for example, two or more servings citrus fruit or juices per day associated with an 18% lower risk of depression, compared with less than one serving per week.
“Direct mechanisms may include modulating signaling pathways responsible for maintaining neuron survival and inducing synaptic plasticity. Indirect mechanisms may include reducing neuroinflammation, improving blood flow, or reducing oxidative stress,” wrote researchers from Brigham and Women’s Hospital and Harvard Medical School (US), the University of East Anglia (UK), and Harvard T.H. Chan School of Public Health (US).
“However, it is unclear whether the different flavonoid subclasses and their metabolites share generic neuroprotection properties or whether particular flavonoids are more neuroprotective than others. It is important to note that, although many flavonoid metabolites are shown to cross the blood-brain barrier, the beneficial effects of specific flavonoids may depend on their bioavailability—influenced by absorption, metabolism, and disposition in tissues and cells—which differs greatly by subclasses.”
The researchers used data for 82,643 women participating in the Nurses’ Health Study (NHS) and Nurses’ Health Study II (NHS II). Dietary intakes were assessed every two to four years using food-frequency questionnaires and depression was either clinically-diagnosed or linked to antidepressant use.
Data collected over 10 years indicated that 10,752 incident cases of depression were documented. Higher intakes of flavonol, flavone, and flavanone were inversely linked to depression risk.
Significant risk reductions of between 9 and 12% were observed for total flavonoids, polymers, and proanthocyanidin intakes but only for older women.
“Although the association estimates were moderate and intervention trials are needed to further understand the clinical importance of these findings, several points can be highlighted,” wrote the researchers in the AJCN. “First, despite modest effect estimates, at a population level the results may be important. By using a population-attributable risk framework, 5% of the depression cases that occurred in both the NHS and NHSII could have been prevented if all women in the lowest 3 quintiles of flavanone intakes switched to the highest 2 quintile of intakes.
“Second, although the magnitudes of overall estimates of association were modest in the primary analysis, the associations were stronger with respect to late-life depression. For example, women in the highest quintile of flavones and proanthocyanidins showed a significant 17% reduction in the risk of late-life depression.
“Third, the significant dose-response relation and consistency across 2 cohorts for several specific flavonoids made the observed inverse associations less likely to be due to chance.”
They concluded: “Further prospective studies and intervention trials are needed to confirm these associations. If confirmed, the findings may have important implications for depression prevention, because there are limited, readily-modifiable risk factors for depression.”
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi:10.3945/ajcn.115.124545
“Dietary flavonoid intake and risk of incident depression in midlife and older women”
Authors: S-C. Chang, et al.