What affects the quality and quantity?
Effect: Most drugs pass through breast milk to some degree.
What to do: Ask your doctor about the safety of any medication you want to use, including herbal supplements. Follow directions for pain relievers like ibuprofen and acetaminophen, but avoid aspirin. Most OTC antihistamines/decongestants are safe but may lower milk production. If your supply decreases, drink lots of fluids and talk to your doctor about alternatives.
Effect: Infants breastfed by vegetarian moms may be lacking in vitamin B12, since meat, poultry, and seafood are big sources.
What to do: Get at least 2.8 micrograms (mcg) of vitamin B12 daily through a multivitamin or food. If you eat eggs and dairy foods regularly, you may be fine - a cup of skim milk has 1 mcg, and one egg has .5 mcg.
Effect: Alcohol transfers to breast milk and changes its odor and taste. Two drinks a week can decrease your supply or make your baby less alert.
What to do: It's best not to drink. If you do, limit yourself to a very occasional celebratory drink, after nursing.