Many people were reassured by my recent post on re-freezing breast milk, but also wondered about long-term freezing. Can you use breast milk after more than a year in the freezer?
As in the question of re-freezing, this isn’t that difficult to answer and it’s medically relevant due to the use of donor milk. So we have reasonably good evidence, which generally suggests some small loss in nutritional value (namely, fat) from longer in the freezer. See, for example, this study of 150 samples and this review article. There is some inconsistency in the review about moderate versus deep freezing. And the evidence is a bit incomplete. Specifically, they do not typically evaluate freezing beyond 6 months.
There’s nothing to suggest long-term frozen breastmilk will harbor pathogens, but it seems likely that there is some degradation of nutrients. I will say these figures are small — say, 3 to 10%. Put differently: if you feed your baby milk that has been frozen for 6 months, they might need more.