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In the news: Anti-Inflammatory Dietary Pattern May Lower Risk of Depression

Inflammation and Depression

According to the World Health Organization, depression is the leading cause of disability world-wide, and it affects more than 15 million American adults in a given year.

Greater attention is being paid to its role as a major independent risk factor in many chronic illnesses such as heart disease and certain cancers, and it has been associated with ocular conditions as well. Depression and anxiety are reported to be more prevalent in dry eye disease (DED) patients than in controls, for example (1). A recent study also reported that symptoms rather than clinical signs of DED were more predictive of depression in a cohort of female DED patients (2).

There is also increasing recognition that ongoing, chronic inflammation may have a part to play in depression. One investigation, for example, found that people with depression had higher blood levels of the inflammatory marker C-reactive protein (CRP). Brain scans of depressed individuals have also indicated increased neuroinflammation compared to those without depressive symptoms.

Further, dietary factors consistently have been shown to affect inflammation through both pro- and anti-inflammatory mechanisms. The Western-type diet (high in sugar, fried foods, high-fat dairy products, and refined grains) is associated with higher levels of CRP and interleukin-6. In contrast, the Mediterranean diet (high in whole grains, green leafy vegetables, and fish, low in red meat and butter, with moderate alcohol
and moderate to high olive oil intake) is associated with down-regulation of those inflammatory markers.

Pro-inflammatory Diet & Depression Risk

In 2014, a collaborative team from the University of South Carolina and Harvard developed a dietary inflammatory index (DII) as a tool to assess an individual’s diet on a continuum from maximally anti-inflammatory to maximally pro-inflammatory. To test the assessment tool, the team first used the DII to compare three different dietary patterns already linked to pro- or anti-inflammatory effects: fast food diet, Mediterranean diet, and macrobiotic diet which is a modified traditional Japanese diet (high whole grains, vegetables, beans, with lower fish, fruit, and sweets).

As expected, the macrobiotic and Mediterranean diets produced strong anti-inflammatory DII scores vs. the DII score for the fast food diet, which had strong pro-inflammatory potential. Using the DII tool, the researchers have gone on to explore the relationship of inflammatory eating patterns and many chronic diseases such as heart disease and osteoporosis.

In the newest investigation (3), the team looked at a pro-inflammatory diet and the presence of depressive symptoms in a group of over 3,600 participants (mean @ 60 years) with or at risk for osteoarthritis of the knee. The relationship between baseline DII score and incident depression was assessed through Cox's regression analysis, adjusted for potential con-founders, and reported as hazard ratios.

Over an 8-year follow-up, 837 participants developed symptoms of depression. Those consuming the most pro-inflammatory diet were found to have a 24% increased risk of developing depression compared with those eating the most anti-inflammatory diet (HR: 1.24; 95% CI: 1.01-1.53; p = 0.04).

This study adds to the growing body of evidence that at least some forms of depression may be affected by diet. And though interventional studies are needed, the authors suggest that transitioning to a more anti-inflammatory diet may reduce depression risk. For a simple list of foods that promote or counter inflammation, see the Harvard Medical school site: https://www.health.harvard.edu/staying-healthy/foods-that-fight-inflammation.

References

1. References

   1. Wan KH, et al. Depression and anxiety in dry eye disease: a systematic review and meta-analysis. Eye (Lond). 30: 1558–67, 2016.
   2. Gonzales JA, et al. How Are Ocular Signs and Symptoms of Dry Eye Associated with Depression in Women with and without Sjögren's Syndrome? Am J Ophthalmol. Epub ahead of print, Apr 12, 2018.
   3. Shivappa N, et al. The relationship between the Dietary Inflammatory Index (DII) and incident depressive symptoms: A longitudinal cohort study. J Acct Disord. Epub April, 2018.