Vegans must make sure their diet includes enough vitamin B, because it does not occur reliably in plant foods. Vitamin B deficiency can have serious bad effects on the person's health. These might include anemia and neurodegenerative diseases. California-based dietitian nutritionist Ashley Lytwyn said “Nutrients like B12 can be tough to get with a vegan diet, and the iron in vegetables isn’t as bioavailable as iron in animal proteins.” “Even if he ate enough iron-rich vegetables, the body can’t always absorb what it needs.” Vegan societies recommend that vegans either eat foods with added B or take a B supplement. Tempeh, seaweed, spirulina, organic produce, and intestinal bacteria "do not have enough B for a vegan diet". Vitamin D deficiency is possible in the absence of dairy products (which are normally fortified with vitamin D). It can be prevented by supplements, and by direct injections.