B vitamins — especially B12, B6, and folate — become harder to absorb and easier to deplete during perimenopause. The problem: deficiency symptoms (fatigue, brain fog, low mood, tingling) look almost identical to hormonal symptoms. Meanwhile, declining estrogen raises homocysteine, a compound linked to cardiovascular disease, cognitive decline, and bone fracture risk. B vitamins are your primary tool for controlling it. Here's what the research shows, what to test, and what t