I haven't seen the study referred to that found no benefit of lower risk of
SIDS in co-sleeping families.  I would be very surprised if ANY study ever
found this link.  SIDS is extremely rare, so you need a humongous sample
size to discover differences in incidence, and once you get that big of a
sample size, the possibility of there being confounding variables that
obscure the relationship is of course also high.  There is no clear
definition of co-sleeping, either.  Do we mean between the parents, all
night long, every night?  Do we mean with one parent, for part of the night?
Starting out in a crib or bed and finishing the night in bed with mom and
day?  Starting out the night with mom and dad and ending up in a crib or
bed?  How many hours each night?  How many nights each week?  Etc. etc. etc.

Dr. McKenna's work does cite statistics based on national data for different
countries showing that the national rates of SIDS are lowest in countries
that breastfeed and co-sleep, and highest in countries like the US that do
neither.  Except in places like New Zealand, where the co-sleeping moms are
smoking in bed with their kids, where SIDS rates are high.

What Dr. McKenna's work has done in show how mother's and baby's sleep
cycles (he calls it the "architecture of sleep") are coordinated when they
sleep together in the same bed.  When mom is in light sleep, so is baby.
When mom is in deep sleep, so is baby.  When baby experiences apnea in a
deep sleep cycle -- thought to be one of the causes of SIDS -- mom nudges
baby, makes noise, or actually wakes up and jostles baby, and baby rouses.
McKenna's work was done with moms and babies in the same bed or else in
separate rooms -- no dads involved, no research on whether same room but
different bed has the same effect.  He has found that babies spend much less
time in really deep sleep if they are sleeping with mom.  They also nurse
more often and for greater total durations.  Mom opens eyes, looks at baby,
touches baby, rearranges covers on baby, etc., many many times during the
night, often without officially "waking up".

Even if someday a study proves that co-sleeping has NO effect on SIDS -- I
would still highly recommend it, as the species has evolved to expect
co-sleeping, babies are surely more secure and feel more loved when a warm
body is nearby, mother gets more sleep this way, breastfeeding is more
likely to continue longer, and mother's periods to stay away longer, and
it's FUN to sleep with your baby.  Not to mention your six year old.  All
around the world, most people sleep with their children.

Of course, it must be done with common sense, on a suitably hard mattress
(most people in the world sleep on the ground/floor/mat), without tons of
fluffy pillows or covers, and with baby not in danger of falling out of a
high bed or getting stuck between bed and wall or bed and bedframe.  And
parents must be responsible -- not morbidly obese, not drug or alcohol
impaired, etc.

Katherine A. Dettwyler, Ph.D.
Associate Professor of Anthropology and Nutrition
Texas A&M University
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