Vitamin B12
Vitamin B12 is a water-soluble vitamin that is required for red blood cell formation, neurological function, and DNA synthesis. Many animal products contain vitamin B12, including fish, meat, poultry, eggs, milk, and milk products, but it is generally not present in plant foods. Fortified food products include breakfast cereals and nutritional yeast. Dietary supplements containing vitamin B12 are also available, usually containing the cyanocobalamin form.

Low vitamin B12 levels can lead to fatigue, muscle weakness, gastrointestinal issues, anemia, and memory issues.

Vitamin D
Vitamin D is a fat-soluble vitamin that is required for normal bone growth and remodeling. It also plays a role in the reduction of inflammation, modulation of cell growth, neuromuscular and immune function, and glucose metabolism. Vitamin D is naturally present in a few foods, and is produced endogenously when ultraviolet (UV) rays from sunlight trigger vitamin D synthesis.

Low vitamin D contributes to bone, muscle and joint pain, reduced energy, frequent illnesses, and skeletal deformities.

Folate
Folate is an important nutrient that functions as a coenzyme or cosubstrate in various reactions, including the formation of DNA and RNA, and metabolism of amino acids. Folate is naturally present in a wide variety of foods, including vegetables, fruit, nuts, beans, seafood, eggs, dairy products, poultry, and grains. Folic acid is obtained as a dietary supplement and also from enriched bread, cereals, flours, cornmeal, pastas, rice, and other grain products.

Folate deficiency is characterized by fatigue, lethargy, headaches, pale skin, and muscle weakness. Folate deficiency during pregnancy increases the risk of neural tube defects, low birth weight, preterm delivery, and fetal growth retardation.

Ferritin (Iron Stores)
Iron is a mineral with several essential functions in the body. It is required to transport oxygen around the body and is also essential for growth, normal cell function, and the production of connective tissue and some hormones. Good food sources of iron include red meat, beans, nuts, and dried fruit.

Low iron levels can result in anemia, which can have serious repercussions if left untreated, including impaired cognitive function, disturbances in the digestive system, and impaired immunity. Approximately 25% of the iron in a normal adult is present in a storage form, with the most common form being ferritin (accounting for about 2/3 of storage iron). Ferritin analyses provide a sensitive, specific, and reliable measurement for determining iron deficiency at an early stage.