Well yes, Vitamin D is pretty hard to come around in the northern hemisphere so no surprise there. Mind you, it's far not the only thing - magnesium, zinc, selenium are just a few which most people are missing. I mean unless your diet consists entirely of tuna and salmon probably. Over the last few years, I've stressed significantly on my physical health(after being very overweight for the most of my adult life and now happy to say this is not the case anymore at all). And while Vitamin D has been one of the things I've become very strict about, my supplements menu has significantly expanded. And there are plenty of products which come bundled with your daily intake of vitamins and minerals. And one in particular has become a part of my breakfast at this point. I haven't had as much as a sneeze in the last two years, haven't felt even mild fatigue or exhaustion, even after the toughest of days. But as you said, it's best to consult a doctor first, especially if you have bad medical history. If you are healthy and fit though then there are plenty of good options to go with.