SERcadian Rhythms

The amino acid L-serine may be the next melatonin. A new study showed administration of 3 grams ~30 minutes before bedtime advanced melatonin onset dramatically, almost instantly. It didn’t increase the concentration of melatonin, just onset (Yasuo et al., 2017). For a higher concentration, you’d need AM sunlight and PM blue blockers or actual mel supps (preferably the former) (eg, Burke et al., 2013).

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Important and interesting caveat in the L-serine story: it only worked if the participants received bright light in the morning.


In the figure below, “day 1” is no AM light and “day 2” is yes AM light. In both the L-serine and placebo groups, there is a phase advance on day 2 because of the AM light treatment. The advance is markedly greater when the participants received 3 grams of L-serine:


Using rodent models (which mimicked the human effect almost exactly), GABA-A receptors were implicated.

Interesting for a couple reasons.



GABAnergic agents like benzo’s and alcohol don’t really put you to sleep; they knock you out, which isn’t proper sleep. This suggests a non-circadian effect of L-serine; however: 1) GABA-A prevents light-induced SCN activation; and 2) serine advanced melatonin onset (specifically only when combined with light in the morning).

Anyone gonna try L-serine?

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Two important blog posts which may hint at how this happened: LIGHT timing for circadian entrainment and Melatonin sensitizes the system.