Someone asked about peanut sensitization during pregnancy and breastfeeding. 
I think you are probably refering to the 1998 article in the British Journal 
of Medicine entitled: "Women warned to avoid peanuts during pregnancy and 
lactation."

I found an interesting discussion of this issue at: 
http://www.allerg.qc.ca/peanutallergy.htm#sensitization  

Kathleen Fallon Pasakarnis, M.Ed., IBCLC

Peanut allergy: where do we stand?
  
John Weisnagel, M.D.

Sensitization to peanuts

-possible during pregnancy, probable during breast feeding:

The British Medical Journal, June 27th, 1998 published a letter entitled 
"Women warned to avoid peanuts during pregnancy and lactation." that came 
from the Department of Health, Committee on Toxicity of Chemicals in Food, 
Consumer Products and the Environment, Wetherby, North Yorkshire. According 
to John Warner, professor of child health at Southampton University and a 
member of the government's working group on peanut allergy, there appears to 
be a "link between maternal consumption of peanuts and peanut products and 
earlier onset and increasing prevalence of allergy. Evidence from aborted 
fetal samples shows that from the second trimester onwards fetuses are 
capable of producing an allergic reaction. There are several theories on how 
sensitization occurs. Some research shows that antigens from the mother can 
cross the placenta, whereas other work suggests fetuses can swallow IgE from 
the amniotic fluid, causing sensitization 31. 

Following the June 27th, 1998, article in the British Medical Journal, a 
comment was published in The Lancet by Pamela W Ewan, July 4th, 1998, 
entitled "Prevention of peanut allergy" in which she notes that the 
Committee's report said that pregnant women "may wish" to avoid eating 
peanuts...she stresses the importance of peanut allergy as a common cause of 
anaphylaxis...its prevalence having increased substantially32 ...regarding in 
utero (during pregnancy) sensitization, there is a lack of convincing 
evidence from prospective studies that manipulation of the maternal diet 
during pregnancy has a lasting effect on the development of food allergy. 
Indirect data suggest that lactation is a more likely route of primary 
sensitization, but this point remains to be established34. 

In the Aug 29th, 1998 issue of The Lancet, Deborah E Fox, Gideon Lack, as 
well as Richard S H Pumphrey, Phillip B Wilson, and Amolak S Bansai, respond 
to Pamela Ewan's commentary. The first letter agrees with Ewan's call for 
further studies 'so that these public health measures can be soundly 
based'...the UK guidelines ..have caused distress to mothers with 
peanut-allergic children. The second letter authors suggest that the advice 
of the Committee be extended to all nuts 35. 

In a Feb 1999 study done in Cape Town, South Africa79, it was shown that: 
mothers who consumed peanuts more than once a week during pregnancy were more 
likely to give birth to a peanut-allergic child than mothers who consumed 
peanuts less than once a week. 
Peanuts or peanut butter was introduced into the child's diet from a 
significantly younger age in the peanut-allergic subjects. 
There was a positive correlation in the peanut-allergic subjects between age 
of introduction of peanuts and age at the onset of symptoms. 
Exclusive breast feeding did not protect against the development of peanut 
sensitization. 
Peanut allergy is associated with an increased risk of sensitization to other 
foods. (posted Aug. 6th, 1999) 

In the June 2000 of the Anaphylaxis Network Newsletter, Dr Peter Vadas, past 
President of the Anaphylaxis Foundation of Canada, and the Medical Director 
of the Regional Anaphylaxis Clinic at St Michael's Hospital in Toronto, 
writes in his article on 'The Process of Sensitization', "A study just 
completed in my laboratory has shown that peanut protein does, in fact, pass 
from the maternal diet via the bloodstream into breast milk. Using a very 
sensitive assay for peanut allergens, we tested samples of breast milk for 
the presence of peanut protein at various times after consumption of dry, 
roasted peanuts by a group of volunteers. The two major peanut allergens 
associated with anaphylaxis were detected in breast milk within one to three 
hours after ingestion in approximately 50% of the volunteers. These data 
confirm the previously unproven notion that some infants may become 
sensitized by exposure to peanut protein through breastfeeding." The study Dr 
Vadas refers to has just been published in the April 4th, 2001 issue of the 
Journal of the American Medical Association 115 (posted April 14th, 2001)  Dr 
Vadas continues, "However, the story is not quite so simple. The 
concentration of peanut protein, timing of exposure and frequency of exposure 
may lead to either allergic sensitization or to tolerization. The latter 
process actually protects against allergies. In some cases, exposure to 
peanut protein in breast milk may actually protect against later development 
of peanut allergy. At this stage, it would be overly simplistic to suggest 
that all lactating women avoid peanut products during breastfeeding. While 
this may protect some children from peanut sensitization, it may predispose 
other children to acquiring peanut allergy by preventing the process of 
tolerization. Instead, it may be more prudent for lactating mothers to avoid 
peanut products while breastfeeding hight risk infants, namely those who have 
a strong family history of allergies or those who already have a first degree 
relative with peanut allergy. (posted July 26th, 2000)   

The concept of tolerization, or tolerance, was touched upon by Drs Gideon 
Lack and Jean Golding, in their comments regarding Pamela W. Ewing's article 
entitled 'Clinical study of peanut and nut allergy in 62 consecutive 
patients: new features and associations.' BMJ 1996;312:1074-8 (27 
April)...."exposure to peanuts and other food allergens during lactation and 
childhood may be important in the development of immunological tolerance and 
may prevent allergic sensitisation to these foods...avoidance measures would 
serve only to reduce exposure to peanuts to low levels, and this could 
pardoxically increase allergic sensitisation to peanuts; low dose exposure to 
allergens (rather than high dose exposure) favours production of IgE, and as 
little as 2 µg of inhaled allergen a year may be sufficient to induce 
allergic sensitisation via the airways." (posted July 26th, 2000)96 

Other possible sources of sensitization:
How about peanut oil in vitamin A and D preparations? According to a Feb 1999 
Swedish study, sensitization to peanut during childhood through consumption 
of vitamin A and D in oil-based solution seems unlikely.78 (posted Aug. 6th, 
1999) 

Another suggestion is that sensitization might occur by contact with the 
skin, through the application of creams containing arachis (peanut) oil for 
eczema, or nipple ointments in mothers during breast feeding as reported by 
Lack G, Fox DES, Golding J, at the AAAA&I Annual meeting in Washington, DC, 
March 1998. (posted Aug 6th, 1999)  






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