• Women who wore their bras 24 hours per day had a 3 out of 4 chance of
  developing breast cancer (in their study, n=2056 for the cancer group
  and n=2674 for the standard group).
• Women who wore bras more than 12 hour per day but not to bed had a 1 out of 7 risk.
• Women who wore their bras less than 12 hours per day had a 1 out of 152 risk.
• Women who wore bras rarely or never had a 1 out of 168
  chance of getting breast cancer. The overall difference between 24 hour
  wearing and not at all was a 125-fold difference.

The results of this study are compelling, even considering that it was
not a "controlled study" for other risk factors. Bear in mind that known
(published in medical journals) risk factors for breast cancer are
mostly in the range of less than three-fold differences. It should also
be noted that Singer and Grismaijer surveyed bra-wearing behavior of the
past, which is excellent for a disease with such a long development
period. In their book, the authors show how most of the known risk
factors can be related to bra-wearing behavior and/or the lymphatic
system.

For example, breast feeding and pregnancy cause full development of the
mammary lymphatics. Also, women of higher economic status have higher
breast cancer rates, and one would expect that they would wear their
bras more hours per day. Women who excercise have lower risk, which
could relate to better lymphatic circulation (and I would add, more
breast movement).

To this discussion, I would like to add that lymphatic circulation in
many tissues (especially the primary lymphatics) are highly dependent on
MOVEMENT. When you sit for a long time on an airplane flight, your feet
and ankles can swell, because lymphatic circulation goes to near zero.
Wearing a bra, especially a constricting one with underwires, and
especially to bed, prevents normal lymphatic flow and would likely lead
to anoxia (lower than normal oxygen content), which has been related to
fibrosis, which has been linked to increased cancer risk.

Women evolved under conditions where there was BREAST MOVEMENT with
every step that they took when they walked or ran. My reading of the
scientific literature about lymphatic flow shows me that this may be as
important as the constriction factor. Every subtle bounce of the breast
while moving, walking, running, etc. gently massages the breast and
increases lymphatic flow and thus cleans the breast of toxins and wastes
that arise from cellular metabolism.

Of course, there may be other mechanisms for the damage that bras
apparently cause. One such mechanism could be temperature. Breasts are
external organs and have a naturally lower temperature. Cancers can be
temperature-dependent. Breast cancer is hormone-dependent. Temperature
can alter hormone function. Breast temperature changes throughout the
monthly cycle.

All these facts are from the medical literature. By whatever mechanism,
someone will eventually explain why Singer and Grismaijer found a
125-fold difference in cancer rates between bra-free breasts and those
constricted by 24-hour-per-day bra-wearing.

If you haven’t already done so, I suggest that you read the book by Singer and Grismaijer ( Dressed to Kill,Avery Press, 1995). (By the way, I have no connection to the authors; I think that they live in Canada.)

Also, just for an interesting experiment, the next time you walk down
the street, notice visually how constricting bras are. On many women you
can actually see "dents" around the sides of their chests where there
bras are, even in something as opaque as a black t-shirt.

A physical therapist friend of mine, after reading Dressed to Kill,
said that she was amazed at what she saw in her practice at a local
medical clinic. She noticed how many women have red creases and grooves
on the their bodies caused by their bras. Singer and Grismajer also
suggest that you simply stop wearing one for two weeks and see how you
feel.

By the way, I have heard that they are currently working on a new study.
The research is to study whether benign fibrocystic breast disease can
be treated by stopping bra-wearing for eight weeks. That should be very
interesting; this time they are involving medical doctors, from what
I’ve heard.

Years ago, many people thought that the idea of cigarettes causing lung
cancer was funny. Even if further research with highly controlled
studies only shows a difference of 5-fold, or even 2-fold, it will be no
laughing matter.