You might be reading this in the pouring rain or freezing cold, wondering whether this weather is cause for loading up on vitamin D (if you're anything like me, you haven't spent any real time in the sun in months!!). Not only is the vitamin essential for bone strength and overall immunity, but it's key for skin health (a deficiency is associated with acne). It's estimated that 1 billion people worldwide have a vitamin D deficiency. But like so many other things, the misinformation out there is mind-boggling. How much of this vitamin do we actually need? Where do we get it from? And how can we know if we're lacking? I turned to Alexandra Caspero, MA, RD, CLT, RYT, and a nutritionist at HUM (a brand that makes a curated selection of vitamins and supplements), to fill us all in.