Hack Your Biological Clock: Light-Induced Circadian Phase Shifts Work So Well That You Better Watch Out to Avoid Accidental Phase Shifting When You Check Your Mails

If you do it on purpose, "hacking" your biological clock can be highly beneficial. If you're doing it out of pure ignorance, though, you're in trouble.

In view of the impeding return to standard time, it's probably a good thing, in view of the iPhones, iPads and Facebooks of this world it could turn out to be a serious health problem, though: the ease with which you can "hack" your biological clock - on purpose, but also incidentally.

How easy it really is to turn the biological clock of life forward and backward has in fact only recently  been confirmed by Seong Jae  Kim and colleagues from the Northwestern University Feinberg School of Medicine and the Technology Evaluation Center of BlueCross BlueShield Association (Kim. 2013)

Fast forward / backward, please!

All the scientists had to do to make sure that the 29 healthy young (25.1 ± 4.1 years, M:F=8:21) and 16 healthy older subjects (66.5 ± 6.0 years, M:F=5:11) who participated in the said study experienced a 2h shift in the onset of their natural melatonin release was to expose them in a randomized order to 2h light pulses of 2 different intensities: 2,000  and  8,000lux)

Figure 1: Graphical summary of the implications you of the data from Kim et al. (2013)

As you can see in the graphical illustration of the implications in Figure 1 the scientists used the core body temperature minimum (CBT_min) of their subjects as a reference.

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"Subjects were admitted for four nights and three days under dim light during daytime hours with eight hours of sleep in dark at their habitual time (dark bars). Blood samples were taken throughout the baseline and post -treatment nights to assess lightinduced [sic!] changes in the circadian melatonin rhythm.

On the third night, subjects were exposed to light at one of 3 time points ( -8h, -3h, or 3h) relative to the core body temperature minimum (CBTmin) measured on the baseline night. They were exposed to a 2-hour light pulse (including a 15 min ramp up and ramp down) of 2,000 lux on one laboratory stay and 8,000 lux on a different laboratory stay, in a randomized order, separated by at least 3 weeks." (Kim. 2013)

I guess it may come as a surprise that the scientists were able to show that the effect size / efficiency of the procedure was significantly influenced by the time of pulse, but not by its intensity, the age of the subjects or interactions between age and intensity, or time of pulse and intensity.

What did make a difference, though was the lag (=length of the time shift that was achieved), though.  Administered -8h before core body temperature minimum (CBT) the average phase delays  were -0.72h for  2,000lux and -0.50h for  8,000lux. When it was administered +3h after the CBT the researchers observed only a minimal phase advance of +0.05h for  2,000lux, while the 8,000 lux light produced a phase shift of + 0.18 h. In both cases the standard deviations were however so large that a significant difference could not be found.

8h is where the sweet spot it + phase advances are difficult to achieve

The "wake-up protocol" (Figure 1, 2nd row on night 3), in the course of which the subjects were woken up 3h before the CBT and thus while they were already sleeping had paradoxical and unpredictable effects:

"Light exposure targeted 3h before CBT min was distributed in both phase delay and advance regions  (-3.2h to +2.5h) relative to the melatonin midpoint." (Kim. 2013)

Needless to say that this is not a suggested protocol, but a good example of the mess that happens, when your sleep gets interrupted by light exposure.In other words, the procedure is identical irrespective of your age and the "power" of the lamp you use - the one thing that counts is the timing of the pulses.

In the discussion of their results, the researchers point out that their findings are in line with previous studies by Duffy et al. (Duffy. 2007), ...

"[...]who found that there was no difference between young and older adults in the magnitude of  phase delays of the melatonin rhythm following 6.5 hour light exposure of more than 1,000 lux." (Kim. 2013)

They also reference a study by Sletten et al. (2009) that compared the effectiveness of blue and green light in young and older adults. In the said study, the researchers determined that the phase advances in response to blue light were  slightly larger than advances in response to green light in both young and older adults. The perceived effects on subjective alertness and sleepiness, on the other hand, were significantly more pronounced in the younger participants in the blue light condition.

As Kim et al. point out, their own previous analysis seem to indicate that blue light is much more effective, when it comes to the induction of phase advances than green light - in fact, in one of their studies, the exposure the use of green and red light did not yield satisfying results at all (Green. 2004).

So does this mean you have to use one of the fancy blue-light lamps?

Despite the fact that there is little doubt that "blue" (~430nm) light is more effective than green light and that red light does not work at all, you may be shocked to hear that running Facebook on your laptop screen is probably enough to get the job done.

The reasons are simple: Firstly, what you see there is "blue" or at least "blueish", anyway. More importantly, however, the fancy LCD and LED displays in modern notebooks, tablet PCs and smartphones have an outstanding luminosity (=they are bright enough) and, as you can easily see in the graphs below, "blue enough".
The spectral data does also tell you that you will never "lack" blue light to convince your body that it's time to rise and shine, not time to sleep, even if you have one of the modern "true color" displays. Much contrary to the clock in the lower right of your screen, your biological clock will thus basically freeze in "daylight mode" the very moment you sit down in front of your screen.

Yes, things can become worse - you don't even have to sit there for hours

I know what you're thinking, you, a SuppVersity Veteran from hour one, obviously new all that and the only thing you do after 8PM, to make sure you can be in bed ad 10PM and get your 8h of sleep before you have to shower at 6AM on the next morning is to check the occasional text massage on your phone, right? Well, bad news:

"According to published data, a phase shift is often not completed immediately after a light pulse (Pittendrigh et al., 1958; Watanabe et al., 2001)." (Kim. 2013)

Actually the saturation effect, i.e. the presence of identical phase shifts for 2,000 and 10,000 lux, confirms it: It does not take hours to biohack yourself!

It goes without saying that this is a good thing, if you actually plan to advance / delay the onset of melatonin release, it is however a serious problem if you "just head back to check your emails" right before you are heading to bed.

References:

• Longo DL et al. Harrison's Online. Featuring the complete contents of Harrison's Principles of Internal Medicine, 18e.
• Kim SJ, Benloucif S, Reid KJ, Weintraub S, Kennedy N, Wolfe LF, Zee PC. Phase-shifting Response to Light in Older Adults. J Physiol. 2013 Oct 21. [Epub ahead of print]
• Sletten TL, Revell VL, Middleton B, Lederle KA, Skene DJ. Age-related changes in acute and phase-advancing responses to monochromatic light. J Biol Rhythms. 2009 Feb;24(1):73-84.