Although vitamin deficiencies and their associated adverse effects are usually considered a public health problem in the developing world, they remain an important clinical consideration for select populations across the globe. In fact, there is concern that we may be confronted with increased negative consequences of poor nutrition due to decreased testing and screening and less education in our medical institutions about the importance of good nutrition to optimal health. (1)
Casimir Funk, PhD, discovered that key nutrients, which he termed vital amines, are essential to maintaining good health and that deficiencies in these key nutrients led to pathognomonic disease states. This realization was a result of observing birds that were fed a diet of polished rice and developed a diffuse polyneuritis (beriberi). The same birds were then fed a diet of brown rice, and their "nervous symptoms rapidly disappeared." (2) This experiment helped establish the importance of vital amines, later shortened to "vitamin."
Vitamins can be broadly delineated into water-soluble and fat-soluble categories. Water-soluble vitamins are typically absorbed very quickly via the gastrointestinal tract and widely distributed in various tissues throughout the body. However, because these vitamins are water soluble, they are not efficiently stored in tissues. Therefore, this class of vitamins requires regular consumption (either through diet or supplementation) to avoid deficiency. Conversely, fat-soluble vitamins are more easily stored, typically in adipose tissue; therefore, they require less frequent intake. (3) Examples of water-soluble and fat-soluble vitamins can be found in Table 1. (3)
What Is Vitamin [B.sub.9]?
Vitamin [B.sub.9], also known as folate or folic acid, is crucial for DNA synthesis and repair, as well as the metabolism of amino acids involved in methylation reactions. (4) In women who are pregnant, folate deficiency can lead to neural tube defects in the fetus. (5) In adults, folate deficiency can result in multiple neuropsychiatric symptoms. These symptoms may include cognitive impairment, insomnia, psychosis, depression, peripheral sensory deficits, and weakness. These manifestations are very similar to those of vitamin [B.sub.12] deficiency. In patients with depression, folate deficiency can contribute to severity and can impede depression treatment. (6)
What Causes Folate Deficiency?
Folate, which is absorbed in the small intestine, is obtained via diet or supplementation. Select food sources of folate or folic acid can be found in Table 2.7 Most serum folate is found in its active form, methyltetrahydrofolate (methyl THF). Methyl THF undergoes a [B.sub.12]-dependent enzymatic reaction, donating its methyl group to form tetrahydrofolate, which, in turn, is...