Turning 40 isn't a medical switch that suddenly makes your body deficient - but it is a time when subtle shifts in hormones, bone density, muscle maintenance, and sleep start to matter more. Instead of falling for marketing hype, this guide helps you understand what actually changes after 40, which nutrients (like calcium, Vitamin D, magnesium, and Omega-3s) genuinely deserve your attention based on your diet, and how to choose supplements wisely without wasting money.