Tag Archives: prolactin

It’s paleo: Hypothyroidism impairs reproductive success in bitches.

Kisspeptin was discovered in Hershey, Pennsylvania, and was named after Hershey’s Kisses.  It has 776 pubmed citations going back to 2001, and may (or may not) play a key part integrating circannual reproduction patterns and seasonal thyroid function.

Kisspeptin was originally identified as a protein that inhibited breast cancer and melanoma.  This might also provide insight into the WHO’s recent declaration of shift work as a “probable” carcinogen.

Exhibit A. TSH restores a summer phenotype in photoinhibited mammals via the RF-amides RFRP3 and kisspeptin (Klosen 2013)

In this study, TSH infusion in short-day adapted hamsters (who are in winter non-breeding mode) induced summer phenotype & kisspeptin.  It also fattened them up a bit.  These TSH secreting neurons express melatonin receptors, but not those for TRH or T3 (Klosen 2002), so it is said to go something like this:Kisspeptin feedback diagram

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Paleo breeding: mating in the wild.

I’ve adapted much of this chart from Howell-Skalla (2002)  and Tsubota (1998).

Canadian polar bears: bona fide seasonal breeders.circannual hormones

The light cycle increases until June, then decreases until December.  Melatonin goes in the exact opposite direction. Testosterone peaks around the onset of breeding season (springtime, April/May), coinciding with LH (as expected). There is also a lot of bear-on-bear violence at this time due to: 1) testosterone-induced aggression; and 2) the high female:male ratio –-> females rear their cubs and are thus out of the game for about 3 years, but males like to breed every year.

Females followed a similar pattern, with estrogen peaking around breeding season and prolactin following the light cycle.

The authors mentioned that prolactin levels mirrored day length, and according to Wiley this would be the prolactin peak that normally occurs when you’re sleeping, but has spilled over into the daytime due to short sleep / long light cycle… not total prolactin levels (24h AUC?), which should be highest in winter (see below).

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Lights Out! Get your melatonin.

From T.S. Wiley’s website:
“People spent summers, before electric lights, sleeping less & eating heavily in preparation for winter because the light triggered the hunger for carbohydrates. Now, light is available 24 hours a day. Heating and air-conditioning climate control our hormonal responses to consume carbohydrates now available year round. This is the scenario for obesity, Type II diabetes, and depression… In Wiley’s opinion, sleep is the best medicine.”

And Wikipedia:
“Wiley’s main thesis in Lights Out is that light is a physiological trigger that controls dopamine and hormones like cortisol. Wiley posits that with the extension of the natural day through artificial lighting, rest at the hormonal level is rarely adequate for optimum biological needs of the body. In her view, this results in both fatigue and unnatural appetite, which leads to weight gain, exhaustion, and disease. Wiley theorizes that the body’s responses are cyclical, reflecting the seasons of the year, and that the body’s needs vary seasonally. According to Wiley, during the winter months the body needs more sleep, and carbohydrates should be restricted as they would have been naturally during hunter-gatherer times.”


Most of the first third of Wiley’s book “Lights Out: Sleep, Sugar, and Survival” centers around light exposure, melatonin, and the many, many effects of a screwed up circadian cycle.  Jane Plain and Jack Kruse have written volumes on the subject, please see their websites for more in-depth analyses and practical applications…

Much of this blog post is my take on that first third (I couldn’t wait to finish it before writing about it), plus a little input from Google, Pubmed, et al; some commentary & pseudo-fact-checking as well.  I’m going to finish the book, and hopefully it will inspire a few more blog posts as opposed to a tin foil hat.  Most of the stuff in Lights Out makes incredibly good sense, but: 1) that doesn’t mean it’s true; and 2) the strings of logic are far too long to do a proper fact-check.  But really it’s how well it makes sense (mostly) that has me intrigued.

divide and conquer

Melatonin is a sleep-inducing hormone controlled by the light-dark cycle.  It is known.  On the day-to-day, melatonin increases at night and decreases during the daytime.  From Wiley: on a seasonal level, longer days during the summer meant less melatonin overall during these months.  Since melatonin suppresses sex hormones (inconsistent? Eg, Smith et al., 2013), summer is supposed to be breeding time, so the baby is born in spring when food is plenty (I’m OK with this now, but will certainly disagree come December).  Melatonin also suppresses metabolic rate, so the decreased daylight and thus increased melatonin during the winter months helped to survive on less food (supported by Marrin et al., 2013).

Disruptions in circadian rhythms royally screws us up.  According to Wikipedia, fireplaces/candles and incandescent bulbs produce less of the melatonin-suppressive blue lights… use these at night in winter?

Antidepressant and circadian phase-shifting effects of light. (Lewy et al., 1987)
Abstract: Bright light can suppress nighttime melatonin production in humans, but ordinary indoor light does not have this effect. This finding suggested that bright light may have other chronobiologic effects in humans as well. Eight patients who regularly became depressed in the winter (as day length shortens) significantly improved after 1 week of exposure to bright light in the morning (but not after 1 week of bright light in the evening). The antidepressant response to morning light was accompanied by an advance (shift to an earlier time) in the onset of nighttime melatonin production. These results suggest that timing may be critical for the antidepressant effects of bright light.

Next:  Prolactin inhibits sex hormones, and melatonin stimulates prolactin (supported by Gill-Sharma 2009Campino et al., 2008).  Thus, less melatonin in summer means less prolactin = more sex & fertility.  She also says day sex is more likely to result in conception compared to night sex for this reason (couldn’t find a reference for or against this).

Dopamine inhibits prolactin, whereas TRH & melatonin stimulate it.  Melatonin also blunts ACTH-induced cortisol secretion (supported by Torres-Farfan 2003Campino 2008).  Winter = high melatonin, prolactin, and low cortisol & dopamine.  Summer = high dopamine & cortisol, and low melatonin & prolactin.  Prolactin is supposed to be high in winter, during pregnancy; low dopamine would support this.

Circadian rhythm

Dopamine is a summer hormone?  Lu et al. (2006) showed high dopaminergic activity was associated with light and wakefulness (ie, summertime).  However, Venero (2002) showed melatonin stimulated dopamine synthesis in specific brain regions, and Eisenberg (2010) showed increased dopamine synthesis in fall & winter relative to spring and summer.  Two  possible confounding factors come to mind: 1) Location, location, location!  Some of these discrepancies may be due to brain region-specific dopamine metabolism… actually, Lu is the only odd-man out, so perhaps dopamine is a winter hormone?  And 2) Wiley’s main premise is that we pwned the light… epigenetics and the like mean that we, including the people in those studies, have deeply screwed up light/dark summer/winter metabolic programs on an epigenetic level, so it’s possible those studies are riddles with artefacts.  However, Wiley also says that people get sick because they live in perpetual summer (lights on all the time = high dopamine), and Markianos (2013) showed elevated dopamine metabolites in overweight patients; in my experience these studies usually continuously enroll patients, year-round.

I’m really just blazing through abstracts here – this is why I call it “pseudo-fact-checking;” not to be confused with any degree of academic rigor.

To be continued… (no tin foil hats, I promise) (not yet at least)

calories proper