This article (A), which quotes the findings of this study (B) is another example of the misrepresentation of research. The actual study makes claims not supported by its findings and misrepresents the researched cited within the text.
First, the article title at ScienceDaily (SD) is "PET Scans Help Identify Mechanism Underlying Seasonal Mood Changes." No. They should have used the actual study title "Seasonal Variation in Human Brain Serotonin Transporter Binding." That's strange, I don't see the word "mood" anywhere. Hold on, let me get my glasses. Wait a minute, I don't wear glasses. I can see after all.
Since the rest of the SD article is just quotes lifted from the study, I'll just focus on the study itself. "Indolamines (tryptophan, serotonin, melatonin, and related compounds) have transduced light signals and information on photoperiod into organisms and cells since early in evolution, and their role in signaling change of seasons is preserved in humans. " The study cited for this statement (3) is for melatonin only, an indolamine, not indolamines. Secondly, tryptophan is the precursor amino acid that is converted into serotonin and melatonin (i.e., indolamines are neurotransmitters that are synthesized from tryptophan, a standard amino acid).
"Serotonin is involved in the regulation of many physiologic and pathologic behaviors that vary with season in clinical and nonclinical populations.3-12" Maybe it's just me, but when I read this sentence, I assumed that the 9 studies referenced would support the role of serotonin "in the regulation of many physiologic and pathologic behaviors that vary with season." No. Studies 3-11 establish that seasonal mood changes occur in healthy people and in some clinical populations. Only study 12 has anything to do with the serotonin. The serotonin transporter (SERT) specifically. The words "mood" or "depression" are nowhere to be found in that article. The researchers should have said "there is substantial evidence indicating that moods vary by season in both healthy and clinical populations. The role of serotonin is currently unknown."
"Seasonal variations in peripheral serotonergic markers have been demonstrated in several studies." 3 studies are cited and the studies do support this statement. I don't know if 3 constitutes "several," but at least the above statement is accurate. See, that's what happens when you actually read the work you cite.
"...the seasonal variation in serotonin-related behaviors,3-12" Nope. They cite the same studies where only one is about SERT. I want evidence that seasonal mood variations are "serotonin-related behaviors."
"Previous investigations19-20 of regional serotonin transporter binding and season in humans have not led to a clear understanding of the relationship between these 2 measures." That's probably due to the fact that those two studies cited have nothing to with serotonin binding and the seasons. The first study (19) investigated the effects of MDMA and reduction of SERT. The word "season" doesn't appear in the article. The second study (20) is a review of MDD and AD imaging studies. Again, the word "season" is not in the article. Later, they cite two other studies (21, 22). The first study actually is about seasonal SERT changes while the second article focused on that topic secondarily. Maybe the researchers intended to cite references 21 and 22, instead of 19 and 20.
The researchers reach this conclusions about their study, "Serotonin transporter binding potential values vary throughout the year with the seasons." Yes, I'm with you so far, "Since higher serotonin transporter density is associated with lower synaptic serotonin levels, regulation of serotonin transporter density by season...has the potential to explain seasonal changes in normal and pathologic behaviors." Do you have any leftover "No's" from this post (C)? I suggest that you use them now.
Synaptic serotonin levels cannot be directly measured in vivo. So how is it measured? They measure the presence of its metabolite, 5HIAA. Next fact, 95% of all serotonin is in the stomach (D). So, how is low serum 5HIAA a measurement of brain serotonin? It's not. Make sense now? No? Good, let's move on.
"Higher regional serotonin transporter binding potential values in fall and winter may explain hyposerotonergic [related to low serotonin levels] symptoms, such as lack of energy, fatigue, overeating and increased duration of sleep during the dark season."Actually those behaviors are better explained by low cortisol (E). If cortisol is low, the liver cannot synthesize glucose, which leads to lack of energy, fatigue, and increased sleep. People eat more food (especially those high in carbs) in order to increase glucose, which will give them energy.
Still confused? Read this to learn more about serotonin and mood (F).