Question: "Why would a male be low in calcium?"   You either have something wrong with parathyroid hormone governing your calcium levels, in which case you would want to see a doctor about that, or you have a long-going deficiency of related nutrients.    Not enough calcium and not enough vitamin D should not cause low serum calcium — unless the deficiency has been going on for a very long time and is very bad.   Then again, I don't know what measurement you're referring to. So, maybe the calcium was a tiny bit low, and you remeasure it, and it's not low anymore; it was a fluke.    But if you're talking about confirmed low serum calcium, then nutritionally, I would look at long-standing severe deficiencies of calcium and vitamin D. I'd follow it up with measurements of PTH and calcitriol to better assess the situation.   This Q&A can also be found as part of a much longer episode, here:https://chrismasterjohnphd.com/podcast/2019/02/09/ask-anything-nutrition-feb-1-2019/    If you would like to be part of the next live Ask Me Anything About Nutrition, sign up for the CMJ Masterpass, which includes access to these live Zoom sessions, premium features on all my content, and hundreds of dollars of exclusive discounts. You can sign up with a 10% lifetime discount here: https://chrismasterjohnphd.com/q&a