The water soluble micronutrients consist of the B-vitamins and vitamin A, due to their water solubility they are removed via the kidneys if in excess and so unlikely to cause toxicity, but because they are not stored it is important that a regular dietary source is consumed.
One of the major functions of the B-vitamins is helping the body to yield energy from the macronutrients; carbohydrates, protein and fat. Thiamine, riboflavin, pantothenic acid and biotin form part of a coenzyme (a molecule that associates with certain enzymes) to assist metabolic associated enzymes release energy from various food sources (Whitney, 2011).
Vitamin B6 occurs in three forms; pyridoxal, pyridoxine and pyridoxamine, all three act as a co-enzyme in the metabolism of amino acids. They are able to convert the amino acid tryptophan into the neurotransmitter serotonin, an important hormone involved in appetite and sleep regulation and sensory perception, research has shown that vitamin B6 influences cognitive function (Health Quality Ontario, 2013).
Folate and vitamin B12 are closely related and depend on each other for activation, in collaboration they help cells multiply by making new DNA, these include red blood cells that deliver oxygen and nutrients that allow metabolic pathways to function. Vitamin B12 deficiency can lead to anaemia, when abnormally large red cells are produced that contain low levels of haemoglobin, this impacts the transport of oxygen and symptoms include tiredness, low energy, mouth ulcers and cognitive problems. Vitamin B12 is secreted in the stomach along with a protein called intrinsic factor and together they form a complex which allows transport into the small intestine and reabsorption of vitamin B12 into the bloodstream, this cannot occur without the intrinsic factor. Another cause of vitamin B12 deficiency is an inability to produce intrinsic factor which can lead to pernicious anaemia, this is caused by either an inherited defective gene or if the cells of the stomach are damaged, more commonly seen in older adults (NHS,2023).
The B-vitamin coenzymes work in collaboration and depend on each other to function, it is therefore imperative that an adequate, regular dietary supply is maintained as a deficiency in any will create multiple problems, below is a list of significant food sources:
B1/Thiamine: ham, soymilk, watermelon, acorn squash
B2/Riboflavin: milk, yogurt, cheese, whole and enriched grains and cereals
B3/Niacin: meat, poultry, fish, fortified and whole grains, mushrooms, potatoes
B5: chicken, whole grains, broccoli, avocados, mushrooms
B6: meat, fish, poultry, legumes, tofu and other soy products, bananas
B7: Whole grains, eggs, soybeans, fish
B9/folate: Fortified grains and cereals, asparagus, spinach, broccoli, legumes (black-eyed peas and chickpeas), orange juice
B12: Meat, poultry, fish, milk, cheese, fortified soymilk and cereals
Supplementation should not be required as long as a healthy, balanced diet is consumed but the UK government recommends that women who are pregnant or trying to conceive take a daily dose of 400µg of folic acid until week 12 of pregnancy (BNF, 2023). It is common that deficiency of vitamin B12 occurs in those following a vegetarian or vegan diet, in which case supplementation might be necessary.
References
British Nutrition Foundation, 2023. Vitamins and Minerals – Nutritional Information
Health Quality Ontario, 2013. Vitamin B12 and cognitive function: an evidence-based analysis. Ont Health Technol Assess Ser.;13(23):1-45. PMID: 24379897; PMCID: PMC3874776.
NHS, 2023. https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia
Whitney, E et al, 2011. Understanding Nutrition: 2nd Edition
MLT Nutrition 