I've been vegan for a little over five years now. For the first four years or so, I ate a very healthy vegan diet but didn't supplement with anything other than two teaspoonfuls of ground flax seed on my oatmeal every morning. My health remained perfect. In fact, in my first year, my cholesterol levels, which had been normal but creeping upwards, went down significantly and remained low. In my fourth year, I realized that fortified soymilk and the occasional popcorn with nutritional yeast were not giving me the recommended daily dose of vitamin B12. I found Dr. Greger's nutrition recommendations at: https://nutritionfacts.org/2011/09/12/dr-gregers-2011-optimum-nutrition-recommendations/ and started taking vegan vitamin B-12 and D supplements, along with some algal DHA. My energy levels went up within about a week, and I realized that I had been finding it harder and harder to get up in the morning before I began supplementing. My energy had declined gradually over the years, such that I hadn't noticed the change while it was happening. About half a year after this, after a health scare I will not to go into, I realized that I had not been getting enough iodine. I now think I was borderline iodine-deficient, and that this was starting to cause my estrogen level to be higher than it should have been. (I don't know this for sure, since I didn't have my iodine or estrogen levels measured in blood tests. But I suspect strongly that this was the case, based on what I've read about the consequences of iodine deficiency and on certain symptoms I had been experiencing.) I started taking 1/8 teaspoon of bladderwrack powder every day about a month and a half ago. My energy levels jumped way up for about three weeks and then stabilized. I feel healthier now than I have ever felt in my entire life. In conclusion, I did not suffer from any kind of health problems during my first four years of veganism. Even without supplementing, I believe I was healthier than I would have been as an omnivore. However, in my fifth year, I believe I started to suffer from the effects of vitamin B-12, vitamin D, and iodine deficiency. I am posting this in the hope of helping other long-time vegans out there who may be deficient in these nutrients. I am titling it "Iodine deficiency" because this is the one that really took me by surprise. P.S. For any anti-vegan trolls out there who are tempted to jump on this post as proof of the inferiority of the vegan diet, let me point out that the main source of iodine for omnivores in Western countries is the iodine-based germicide that is used to clean the teats of cows at factory farms.