As we age our levels of B12 decrease as our gut function becomes less efficient. In fact this decrease actually begins at age 50 when the mucus membrane in the stomach begins to thin, resulting in decreased production of digestive enzymes and Hydrochloric acid (stomach acid). Stomach acid is essential for the absorption of B12.
Further to this, hypothyroidism is very common after childbirth and with the demands of parenting, is when many women really notice it. The classic description of postpartum thyroiditis includes a phase known as thyrotoxicosis followed by hypothyroidism.