In terms of health, a vegetarian diet can be quite high in certain nutrients, and low in saturated fat and cholesterol, but a study suggests a vegan diet could actually be the best when it comes to lowering heart disease and blood pressure.  But as compared to other vegetarians, vegans (or strict vegetarians) choose to avoid all animal products—for example, eggs and dairy; this means that they can also have deficiencies in certain things that must be made up with supplements or through other means.
Vegan Diet Dangers
The dangers of the vegan diet are few and far between and are greatly outweighed by the widely-acknowledged benefits. Let's go over 4 major nutritional problems you could face from a vegan diet.
1. Vitamin A
While you'll only find pre-formed vitamin A in animal products, there are certain compounds—you've likely already heard of one, beta-carotene—the body can convert into the vitamin. Because of its role in good vision (night blindness is one of the first signs of a deficiency), immune system health, and cell growth, making sure you get enough is key.  For vegans, there are quite a few vegetable options for getting the A you need, but keep in mind, a poorly balanced vegan diet could lead to not getting enough of the vitamin.
2. B12 Insufficiency
If you're not getting enough B12, you could develop anemia or damage to your nervous system. For vegans, getting enough becomes a little tricky since their only reliable sources are fortified foods and supplements. But even with just enough to prevent the major issues mentioned above, studies suggest too little could also lead to pregnancy complications. 
Many vegans typically only get about 400-600 mg of calcium each day compared to the U.S. recommendations of 1,000 mg each day. While recommendations to increase your milk consumption for your calcium is very outdated, you still need to incorporate as many foods as you can to get enough calcium. If you're eating plenty of green leafy vegetables, like kale, spinach, and mustard greens, you'll be getting enough calcium. Supplementing with calcium can be helpful, but watch out–you want to go for a highly-absorbable option, like calcium orotate, instead of using calcium carbonate or citrate.
4. Vitamin D
And research suggests Vitamin D—necessary for calcium absorption—is also just as important in preventing osteoporosis.  Most vegans won't get any of the vitamin from food sources, so supplementing with vitamin D3–make sure it's vitamin D3 and not vitamin D2–could be crucial for bone health.
Iodine is needed for a healthy thyroid, and getting too little can cause problems with the body's metabolic functions. Because your body can't produce iodine, getting trace amounts in food and supplements are your only options. Keep in mind that one study suggests vegans could have iodine deficiencies due to lower iodine levels in plants. 
The Take Home
True, vegans could be some of the healthiest folks out there, but that's only with the right vitamins and minerals. Supplementation with specific nutrients, like vitamin D3 and iodine, can only improve the quality of your diet, no matter which dietary philosophy you follow.
How do you get the most nutritional value out of your vegan diet? Tell us about it in the comments below.
-Dr. Edward F. Group III, DC, NP, DACBN, DCBCN, DABFM