When one makes a study of evolutionary medicine-type issues (that is, all chronic Western disease mediated by inflammation and diet and lifestyle so far removed from the life our bodies were designed for), the same nutrients keep popping up again and again. Fish oil is a good example. Yes, for heaven's sakes. I'm taking my fish oil. Shut up about it already.
When examining the small unexplored niche of nutritional evolutionary psychiatry, however, another trace mineral nutrient keeps bobbing to the top. This warrants a post, of course (or two, or three). Yup, no surprises here - I'm talking about zinc.
Let's start with the basics. This first bit of info comes from a rather abruptly titled "Zinc and depression. An update." from Poland in 2005. No cutesy titles in Poland! They get down to business. Good. I'm from Texas. I prefer cute yet vaguely threatening, myself (i.e. "Don't mess with Texas" as an anti-littering campaign - Also, driving out in the hill country, a large sign with scarecrow: "No trespassing. We don't call 911.") Gulp.
Zinc is a trace mineral (like magnesium, iodine, selenium, et al) that is essential for our continued life. Turns out that 300 or more enzymes in our bodies use zinc as a buddy to help them do their thing. DNA replication, protein synthesis, cell division - basic, mondo important, reliant on the presence of zinc. And guess what - the highest amount of zinc in our bodies is found in the brain - specifically in our hippocampus and cerebral cortex. Zinc deficiency can therefore lead to all sorts of unlovely consequences, such as ADHD, depression, alterations in behavior, learning, mental function, and seizures.
Turns out scientists of yore did all sorts of horrible tests on rats to figure out how zinc might be related to depression. Antidepressants seem to increase the ability of zinc to work as an anti-inflammatory agent in rat brains, zinc alone seems to be an antidepressant for rats, and the combination of zinc + small amounts of different classes of antidepressants (TCAs and SSRIs) enhanced the ability of the antidepressants to do their thing (helping the rats swim longer in hopeless situations, for example, or endure being held by their tails. Is reality TV really any different?).
Zinc therapy in rats also increases the amount of BDNF in rat hippocampi. Readers of the archives will note I am a big fan of BDNF in the hippocampus. And zinc reduced the fighting behavior of rats (and prisoners) too!
Yes, humans. Turns out Maes (my new hero - churned out a 62 page article on inflammation and depression this year, which I now have in my hot little hands!) discovered that zinc is low in the serum of humans with depression. Also, that low zinc seems to affect inflammation and immunity. Our T-cells (members of the immune system who hunt and kill infection) don't work well without zinc, and seem to release more inflammatory cytokines (IL-6 and IL-1) with low levels of zinc. Also, one of zinc's special actions is to inhibit the NMDA receptor in the brain. In suicide victims, there seems to be an alteration of zinc's ability to affect the NMDA receptor. (Turns out, BDNF + zinc helps calm down the NMDA receptor, leading to antidepressant effects.) Can zinc supplementation have antidepressant effects in humans? You may not be surprised at this point that the answer is yes (1).
There is more, much, much more to the story of zinc and psychopathology, but for now, let's end with good sources of zinc in our diets. Not surprisingly, the best sources of zinc are protein-rich meats, such as beef, pork, lamb, shellfish (especially oysters), chicken, turkey, etc. Pumpkin seeds are also a good non-meat source, and while grains have zinc, the absorption is strongly affected by the phytic acid in grains (2). Vitamin C, E, and B6 help you absorb zinc also. Seems that people with intestinal problems (celiac disease, inflammatory bowel), vegetarians, those with chronic kidney and liver diseases, alcoholics, and the elderly are most likely to suffer from zinc deficiency (3). Intake of more than 50mg a day (both from diet and from supplements) can lead to improper copper metabolism, altered iron function, reduction of HDL and reduced immune function.
More on zinc to come!