Re: Light at night-cancer risk in humans verified

[Jan Hollan <jhollan@amper....muni.cz>]

I'd point out, that the need of
  darkness for sleep
 and the need of
  low enough levels of (shortwave) light during wakeful hours at night
 are rather different matters. Let's not confuse them. Here is my long
summary (available as
  http://amper.ped.muni.cz/jenik/letters/public/msg00204.html
 for later access):


Closed eyes case (sleep)

Eyelids filter out shortwave light quite well, down to perhaps several per
cent. I'd bet that white light illumination of closed eyelids by 3 lx does
not reduce melatonin production in humans. I mean, not even by one per
cent, far below any measurable amount. Even when considering possible
population risks (cancers per one million people), this adverse influence
through melatonin can surely be neglected.

However, 3 lx is a tremendous amount of light to cause a grave sleep
disturbance, through photopic or scotopic transduction. In fact, we have
demonstrated it even by measuring such a faintly related quantity as blood
pressure... (unfortunately, there is but a poster abstract in English on
the issue, the first one of four within
http://amper.ped.muni.cz/noc/english/Can_and_Rhythm.htm,
 -- unfortunately, we did not measure the actual eyelid illuminance).

Most people need good darkness (always below 0.01 lx eyelid illumination)
for healthy deep sleep, that's something everybody knows (direct light
from full Moon is too strong already). Of course, very sleep-deprived
people can fall to sleep in any circumstances, but that's no argument
against a basic human right for no-manmade-light-intrusion during
sleeptime. Natural (or even artificial, as common in many cultures during
daytime) darkness for sleep is a must, regardless of melatonin and cancer
risks.


Open eyes -- a case for yellow filtering

However, with eyes open, 3 lx of white light on them is definitely a
non-tolerable level at night, in terms of population risks. This is a
lesson which follows from that breakthrough paper

 Melatonin-Depleted Blood from Premenopausal Women Exposed to Light at
 Night Stimulates Growth of Human Breast Cancer Xenografts in Nude Rats,
 Blask et al. Cancer Res.2005; 65: 11174-11184,
 http://cancerres.aacrjournals.org/cgi/content/abstract/65/23/11174

It shows that natural blood concentrations at night are vital for reducing
or preventing cancer growth of human cells. They should be not
compromised. And, as we know that photic history plays a role (winter
overcast days indoor eye illuminations can be below 10 lx),

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15240654&dopt=Citation
 Adaptation of human pineal melatonin suppression by recent photic history,
 Smith KA, Schoen MW, Czeisler CA,

(something that is to be expected), any common safe limit of white light
at night into open eyes is to be set rather low. Evolutionally, I'd bet
that 1/4 lx is safe. And I'm saying that even 1/2 lx of eye illumination
is safe (even in a population sense). Or 1 lx of candlelight. This is,
after all, consistent with the Stevens 1987 hypothesis (even poor or
ancient-lifestyle people do use flame as a source of light at night).

This does not mean we have to abandon electric lighting. Fortunately,
there is an option to use faint, filtered light. Recently I wrote an
article for Czech architects on the subject; during writing I realised,
and then tried on myself, that even goggles may be a temporary solution
bought such ones for USD 2 (no perfect filtering, but much better than
none). Just yesterday I found a paper from the beginning of 2005 --
Toronto researchers have proven the efficiency of goggles beyond any
doubt and ``long ago'' already:

   Linkname: Blocking Low-Wavelength Light Prevents Nocturnal Melatonin
          Suppression with No Adverse Effect on Performance during
          Simulated Shift Work -- Kayumov et al. 90 (5): 2755 -- Journal
          of Clinical Endocrinology & Metabolism
        URL: http://jcem.endojournals.org/cgi/content/abstract/90/5/2755

Their indoor illumination was 800 lx, what could translate to some 200 lx
of eye illumination. With goggles filtering all light below 520 nm, the
melatonin suppression was rather small (from an individual viewpoint, of
course still very relevant for populations), without filtering, it was
almost absolute.

Apart from using goggles, there is nothing really new I should add to my
last year poster in Graz,
   http://amper.ped.muni.cz/noc/english/canc_rhythm/g_camer.pdf
 -- night lighting should be devoid of shortwave half of light spectrum.
We have such lighting at home already, it's really comfortable.  Enjoying
blue hues can be easily given up. Some introduction to the new demand for
lighting systems (two or three very different ones are needed indoors)
is within the abstract of that article for architects (its rest is in
Czech),
   Linkname: A Healthy house is to ensure a healthy night!
        URL: http://amper.ped.muni.cz/jenik/domy/svetlo.htm


Even outdoor lighting can be a metabolic problem

Fully shielded HPS one, targeting asphalt, should not be, if people look
downwards (and get mostly less then 3 lx to their eyes). But MH could be,
as well as MV. And even HPS becomes a problem if the ground is covered
with snow (esp. considering possible low winter daytime light exposures).

Apart from yellow goggles, another measure can be recommended, namely a
broad (and long) visor (or a hat) -- to block all unnecessary light coming
downwards to the eyes. There is more to it then just reducing the total
light amount: it has been demonstrated, that the most efficient light is
that which illuminates the inferior nasal part of retina, i.e. comes from
above -- see
   G. Glickman, J. P. Hanifin, M. D. Rollag, J. Wang, H. Cooper,
   and G. C. Brainard
   Inferior Retinal Light Exposure Is More Effective than Superior
   Retinal Exposure in Suppressing Melatonin in Humans
   J Biol Rhythms, February 1, 2003; 18(1): 71 - 79.
   http://jbr.sagepub.com/cgi/content/abstract/18/1/71

and from outer (non-stereoscopic) side -- see
   M. Ruger, M. C. M. Gordijn, D. G. M. Beersma, B. de Vries, and S. Daan
   Nasal versus Temporal Illumination of the Human Retina: Effects on
   Core Body Temperature, Melatonin, and Circadian Phase
   J Biol Rhythms, February 1, 2005; 20(1): 60 - 70.
   http://jbr.sagepub.com/cgi/content/abstract/14/2/116

Such a visor can be useful indoor as well, if there is no better option.
I'm just trying it now (I don't like it, but I never wear visor outdoors
in the daytime, so perhaps it's a matter of being used to it).

Nevertheless, eye illumination from outdoor lighting can be a really
cancer-relevant issue just for those people, who use indoor lighting at
night cautiously. Otherwise it's like with passive and active smoking:
current indoor blue and blue-green illumination levels are mostly much
higher than outdoor ones.

Protecting people from passive smoking is a task for legislators.
Protecting people from more than 3 lx HPS eye illumination (or 1 lx for MH
light) outdoors at night is a much easier one. Precaution goes hand in
hand with climate protection here...


Isn't it a good news? If light is a toxin at night, as it has been proven
to be, we can adapt our handling with it so that its toxicity for human
health will be almost excluded. Let's convert it: from a bad lord to a
good servant. The distinctions between these two possible roles are known
well enough already.

jenik