The problem with mucking about with our biochemistry is that you are never really sure what exactly is going to happen. For most substances there is a a range of acceptable amounts, though the best range may depend upon levels of something else (zinc and copper, for example, or vitamin D3 and A and K2).
Serotonin is a tricky one to figure out. Too high, and we get confusion, high blood pressure, and possibly even psychosis, aggression, stroke and death. Too low, and we get anxiety, violence, suicide, and insomnia. It is obviously important to keep the brain levels within a nice healthy range, and the moment we start changing things up (as with an SSRI like Prozac), the body starts changing the number of serotonin post-synaptic receptors. Homeostasis in a nutshell.
But serotonin has some natural rhythms that could be useful to understand. First off, there is a definite summer/winter variation. Meyer's group in Canada used a PET scan on 88 healthy drug-naive individuals, and found that the serotonin transporter that shuttles serotonin out of the brain was highest during the winter, and lowest during the summer. The researchers felt that the most likely brain trigger to explain the variation was sunlight, though humidity also seemed to play a role (1). (Just reading the introduction to Jackson's Melancholia and Depression, and in the time of Hippocrates, 5th century B.C., melancholia was associated with black bile, autumn, and cold/dry weather).
Here in the northeastern US, there has already been a noticeable decrease in daylight compared to midsummer (humph. Back in Texas we would just be settling in for our second three months of summer). And, sure enough, the number of unhappy phone calls to my office has increased accordingly. This happens every single fall and spring with the changing light.
Why would our brains shuttle serotonin out for the winter? I don't know. Maybe it has to do with seasonal variations in food supply. Serotonin also signals satiety - perhaps we were better off eat more than we ought in the winter when we could get our hands on food, and it wasn't such an issue in the summer when food was likely more abundant. That's a wild guess, really. But I'm sure there's a reason.
There is also a carbohydrate/protein signal for serotonin. The actual mechanism is messy, but let's give it a whirl (2 - Thanks for the link, Jamie!).
If you recall, tryptophan is the dietary amino acid we need to make serotonin. The best source is meat, but when we eat meat, we get a mix of all kinds of amino acids, and since tryptophan is the least abundant, when it competes with all the other proteins for admission into the brain, it tends to lose out. So a high protein, low carbohydrate meal will leave your plasma full of tryptophan but your brain a little low.
Until you add some carbohydrate. Here's the messy part. Unlike some other amino acids, tryptophan is mostly carried around in the blood by another protein, albumin. Eat carbs - insulin is triggered, and proteins are taken out of the blood and pulled into the muscle. Except the mostly-bound tryptophan is immune to insulin's siren call. And the brain transporter for tryptophan doesn't care if tryptophan is bound to albumin or floating free. All the sudden, there is more tryptophan hanging out in the blood compared to the other amino acids, and tryptophan is first in line into the brain for once. From there, it is made into serotonin, and we feel good and relaxed and full and sleepy, at least for a couple of hours until the signal shuts off. Then we crave more carbohydrate.
So what does it all mean? Rob Faigin and others have postulated that having obscene amounts of sugar and carbohydrate over long periods of time can max out our serotonin machinery, leaving us unhappy, carb-craving, and depressed. Anti-low carb diet folks will claim that without carbohydrates, we will not get tryptophan into the brain and we will be depressed. Data has been mixed, with some studies showing high amounts of long term sugar consumption having no effect, some having quite a robust effect on aggression and mood, and there is also the rather infamous study of low carb diets showing more depression after two years (though the low carb diet group started off with twice as many people who were on antidepressant medication).
Some people try to bypass the whole thing and take 5-HTP, which is the immediate precursor to serotonin and can get into the brain pretty easily without the tryptophan insulin shenanigans. A couple of food-mood books recommend this strategy, others are against it - there have been only two acceptable trials of 5-HTP and the results were mixed. 5-HTP is not found in the food supply, so it may be safer to take l-tryptophan itself (it was banned in the US in 1990 due to contamination in the Japanese chemical plant that made it). 5-HTP should not be combined with migraine or antidepressant medication, or with too much vitamin B6. If you have a lot of vitamin B6 and supernatural amounts of 5-HTP in the liver, you can manufacture quite a bit of serotonin to be released into the bloodstream, and you risk giving yourself the symptoms of carcinoid syndrome. (Carcinoids are serotonin-secreting tumors and give you flushing, high blood pressure, and valve calcification. Phen-fen was a serotonin- related medicine too). Serotonin in the periphery cannot get into the brain - only 5-HTP and tryptophan can get into the brain.
Confused yet? Wait until you hear that there are seven subfamilies of serotonin receptors, with subtypes of each subfamily, all of which can be up or down-regulated depending on circumstance.
At the risk of being a hypocrite after yesterday's post, I do take some supplements myself. All are designed to more closely mimic an evolutionary milieu of nutrient-rich food and plenty of sunlight. In that vein I take vitamin D3, a mineral/multivitamin, omega 3 capsules depending on my food for the day, and extra magnesium, as the one issue I had with primal eating was cramps in my feet. Ouch! I haven't yet developed a taste for organ meats, which leaves me needing the multi and minerals, I'm sure. Now this is not what you should take, it is only what I take. Aside from those, I rely on food (grass fed beef, wild-caught Alaskan salmon, pastured or omega 3 eggs, organic poultry, pastured butter, ghee, extra virgin olive oil, coconut milk and oil, some fruit, and tons of vegetables from the local farm. Oh, and some macademia nuts, or the rare Larabar.) Some special paleo mironutrient extras include a sprinkle of dulse or kelp, and Celtic salt. Again - that is, for the most part, what I eat. You eat whatever you want :)