It's very hard to find research data because there is hardly any out there. However, Dr Jack Newman says this;
But it is said that breastmilk has no value after six months.
Perhaps this is said, but it is patently wrong. That anyone (including paediatricians) can say such a thing only shows how ill-informed so many people in our society are about breastfeeding. Breastmilk is, after all, milk. Even after six months, it still contains protein, fat, and other nutritionally important and appropriate elements which babies and children need. Breastmilk still contains immunologic factors that help protect the baby. In fact, some immune factors in breastmilk that protect the baby against infection are present in greater amounts in the second year of life than in the first. This is, of course as it should be, since children older than a year are generally exposed to more sources of infection. Breastmilk still contains special growth factors that help the immune system to mature, and which help the brain, gut, and other organs to develop and mature.
It has been well shown that children in daycare who are still breastfeeding have far fewer and less severe infections than the children who are not breastfeeding. The mother thus loses less work time if she continues breastfeeding her baby once she is back at her paid work.
It is interesting that formula company marketing pushes the use of formula (a very poor copy of the real thing) for a year, yet implies that breastmilk (from which the poor copy is made) is only worthwhile for 6 months or even less (?the best nutrition for newborns?). Too many health professionals have taken up the refrain.
I have heard that the immunologic factors in breastmilk prevent the baby from developing his own immunity if I breastfeed past six months.
This is untrue; in fact, this is absurd. It is unbelievable how so many people in our society twist around the advantages of breastfeeding and turn them into disadvantages. We give babies immunizations so that they are able to defend themselves against the real infection. Breastmilk also helps the baby to fight off infections. When the baby fights off these infections, he becomes immune. Naturally.
There is also this from LLLi.
And if you want actual research papers there are some out there, but they are not light reading!
www.huliq.com/11/81484/childs-body-composition-linked-breastfeeding-duration
www.jpeds.com/article/PIIS0022347607002624/abstract
iadr.confex.com/iadr/brazil07/preliminaryprogram/abstract_112328.htm
journals.lww.com/jpgn/Fulltext/2006/05000/Breast_feeding_Duration_and_Childhood_Acute.18.aspx
And Brian Palmer has shown that breastfeeding is important in oral/nasal development, with regard to Obstructive Sleep Apnea and this oral/muscle development is related to clarity and development of speech.
But all the science on the internet is not going to convince you to carry on if you really want to stop.