Water-soluble vitamin deficiency and toxicity: B9, B12 and vitamin C: Pathology review

35 year old Emily comes to the clinic because she’s been experiencing tingling and numbness in both hands and feet. Emily also mentions that she’s been following a vegan diet for the past 12 years, but she’s never taken any vitamin supplements. You immediately decide to run a blood test, which reveals that Emily has elevated levels of both homocysteine and methylmalonic acid. In addition, a peripheral blood smear shows megaloblasts and hypersegmented neutrophils.

Next comes 38 year old Joseph, who’s complaining about the fact that his gums are swollen and bleed easily. On further questioning, Joseph tells you that he’s been homeless for several years. Upon physical examination, you notice that he is underweight, and has multiple bruises, especially on his legs. You decide to take a look at his scalp, and find tiny red spots associated with small twisted hairs that look like corkscrews.

Based on the initial presentation, both Emily and Joseph seem to have some form of water- soluble vitamin deficiency or toxicity. Water- soluble vitamins include the B-complex vitamins and vitamin C. And just like all vitamins, they need to be derived from food, and inadequate dietary consumption can result in deficiency. So, in a test question, look for individuals who come from lower income countries, are at an advanced age, engage in chronic alcohol intake, or have an eating disorder like anorexia nervosa.

Okay, now, another high yield fact is that water-soluble vitamins get easily excreted in the urine. On the other hand, fat-soluble vitamins get stored in fat cells. And that’s why their toxicity, also known as hypervitaminosis, is much less common than that of fat-soluble vitamins, which instead get stored in fat cells. Keep in mind that hypervitaminosis can indeed occur when there’s excess intake of vitamin supplements, highly fortified foods, or medications containing a vitamin derivative.

Okay, now in this video, we’re gonna be focusing on the water-soluble vitamins B9, B12, and C! Let’s start with vitamin B9, also known as folate, which is mainly found in leafy greens, and nowadays many countries fortify foods like grains and cereals with folate. Now, the folate present in these foods is generally in the polyglutamate form, which means that it’s linked or conjugated to a chain of the amino acid glutamate. However, polyglutamate folate is too big to be absorbed by the gut. So, an enzyme in the jejunal mucosa, called intestinal conjugase, cuts down or deconjugates the polyglutamate residues into the smaller monoglutamate form.