Vitamin C is important for metabolic function and plays a part in many biochemical and physiological processes – as well as enzymatic reactions – in the human body. It is possible to absorb enough vitamin C via a well-balanced diet, but when this is not the case, supplementation may be necessary.
Zinc is a mineral affecting essential processes such as the catalytic activity of enzymes and wound healing. Deficiencies in childhood may come with severe health consequences. Although zinc intake is possible via food, daily supplementation in children is recommended.
Fluoride supports teeth and bone development because it counteracts harmful demineralisation effects. Consequently, fluoride may be supplemented for prevention purposes, but excessive consumption should be avoided.
The B-complex comprises a wide range of vitamins such as vitamin B9 (folic acid or folate) and vitamin B12 (cobalamin). Their functions complement each other and affect enzymatic reactions, energy production, and more. An adequate vitamin B intake is important due to the lack of proper vitamin B storage in the body.
Vitamin C, or ascorbic acid, is a water-soluble organic compound needed for normal metabolic function within the body and the biosynthesis of collagen, catecholamines, L-carnitine, amino acids, and certain peptide hormones. It is an essential dietary component because humans are not able to synthesise it via the glucuronic acid pathway. The vitamin has several biochemical and physiological functions in the human body, largely due to its ability to provide reducing properties in various reactions (EFSA, 2013a). Vitamin C can act as a co-substrate or cofactor in enzymatic reactions; it is involved in the synthesis of collagen (present in skin, bones, teeth and connective tissue) and the metabolism of cholesterol to bile acid, and is also essential for the synthesis of carnitine (EFSA, 2013a).
In addition, vitamin C is considered an antioxidant because it is able to protect the body from the damage incurred by oxidative stress. It is also involved in lipid metabolism (actively participating in the conversion of cholesterol to bile acids) and exerts extracellular functions by protecting LDL particles from being oxidised.
Dietary sources of vitamin C include fruits such as berries, citrus fruits (e.g. oranges), papaya and kiwi fruit, and vegetables such as cauliflower, cabbage and bell peppers. Animal tissues also contain vitamin C, but at a lower quantity. Vitamin C deficiency is associated with scurvy in adults – characterised by symptoms related to connective tissue defects due to the weakening of collagenous structures. In infants, it could be associated with bone tissue defects and impaired bone growth, as well as ossification (Shenkin, 2008). According to EFSA, no tolerable upper intake levels are associated with this vitamin, as no strong evidence points to distinct consequences as a result of overdoses or excessive vitamin C (EFSA, 2013a).
Vitamin C is recommended for supplementation if the suggested dosages cannot be reached otherwise. However, these suggested dosages vary according to the source. Recommendations include:
US Institute of Medicine (2000):
Zinc is an essential mineral with a wide array of vital physiological functions and is ubiquitous within every cell in the body. Zinc is required in catalytic activity of enzymes, and plays a role in immune function, wound healing, DNA and protein synthesis, and even cell division. The mineral also supports normal growth and development from pregnancy to childhood and adolescence (EFSA, 2014).
Dietary sources of zinc include meat, legumes, eggs, fish, grains and grain-based products (EFSA, 2014). There is a lack of data on the health effects of zinc deficiency. However, zinc deficiency is associated with acrodermatitis enteropathica in infants (a metabolic disorder affecting the intake of zinc). Due to its diverse role, deficiency could negatively affect the immune system and other physiological biochemical processes. Although excessive zinc intake has not been thoroughly investigated, it is suggested that it may result in severe neurological diseases associated with copper deficiency (Hedera et al, 2009).
If the required dosages cannot be reached via food intake, daily supplementation of zinc is recommended. The body has no specialised zinc-storage system making supplementation even more important in cases where there is a deficiency (Rink and Gabriel, 2000). Dietary zinc recommendations are set by WHO/FAO, IOM, International Zinc Nutrition Consultative Group (IZiNCG), and EFSA. A review by Gibson et al. (2016) summarised the recommended daily allowances for Zinc according to these organisations (Gibson et al, 2016):
Fluoride is a naturally occurring mineral that is widespread in nature and also abundant in the earth’s crust. Although fluoride is not essential for healthy growth and development, in the body, fluoride is associated with calcified tissues such as teeth and bones. As such, the mineral has been used to control the development of dental caries for hundreds of years (Sampaio and Levy, 2011). Fluoride is not essential to teeth development, but exposure to fluoride provides mineralisation benefits, making it less likely that caries will form. The visible part of the outer layer of a tooth (enamel) loses mineral crystals every day. The loss of these minerals is named demineralisation, which causes tooth decay. Demineralisation is also exacerbated by bacteria in plaque that feed on sugars and produce acid – causing tooth decay. Fluoride strengthens the teeth by promoting tooth remineralisation and also by stopping bacteria from producing acids (EFSA, 2013b). Fluoride has also been identified as being an effective anabolic to promote bone health. Fluoride is able to increase spinal bone density by increasing bone formation, and not reducing bone mineralisation. This bone-forming effect is mediated by an increase in osteoblast proliferation (Lau and Baylink, 1998).
Dietary sources of fluoride include meat, fish, eggs, and some soups and teas. Oral exposure to fluoride can also occur through water, including artificially fluoridated water, but also tap water, as some countries have water fluoridation programmes (e.g. Australia, Chile, Ireland, Israel, or the United States) (EFSA, 2013b). Additional sources include supplementation or prescription fluoride, as well as many toothpastes, rinses, and tablets. Fluoride deficiency has not been identified in humans yet. However, as previously stated, lack of fluoride intake may result in susceptibility of the enamel to acid deterioration and therefore causes tooth demineralisation. On the other hand, excessive consumption of fluoride can cause gastric and kidney disturbances, and interferes with calcium metabolism and enzyme activities, which can be lethal to small children (Whitford, 2011; Lech, 2011).
Fluoride is recommended for prevention purposes. Daily intakes and dietary reference values (DRV) are recommended by several distinct health organisations. EFSA has compiled a comprehensive table summarising the recommended DRVs from the following organisations: the Deutschland-Austria-Confoederatio Helvetica (D-A-CH), the Agence française de sécurité sanitaire des aliments (Afssa), the US Institute of Medicine of the National Academy of Sciences (IOM), and the UK Department of Health (DH) (EFSA, 2013b). Apart from the recommendation ages, the major difference lies in the fluoride content of drinking water in the respective countries.
In 2010, the American Dental Association also recommended a dietary fluoride supplement dosing-schedule for children at high risk of developing caries (Rozier et al, 2010). A summary of the most important clinical recommendations is available below:
Below 0.3ppm of fluoride concentration in drinking water:
Between 0.3-0.6ppm of fluoride concentration in drinking water:
Above 0.6ppm of fluoride concentration in drinking water:
The B-complex vitamins are organic water-soluble nutrients that are involved in vital physiological functions and are significant contributors to optimal health, growth and development. For this purpose, they have interrelated roles in cellular functioning, act as coenzymes for enzymatic reactions, and are prevalent in numerous processes including energy production, nucleic acid synthesis and repair, and synthesis of signalling-molecules (Kennedy, 2016).
The complex or group of vitamins usually includes thiamine (vitamin B1), riboflavin (vitamin B2), niacin (vitamin B3), pantothenic acid (vitamin B5), pyridoxine (vitamin B6), biotin (vitamin B7), folic acid or folate (vitamin B9) and cobalamin (vitamin B12). Some authors also include choline , inositol (vitamin B8) and para-aminobenzoic acid (Schellack et al, 2015). The vitamins of this group play a role in several different physiological mechanisms and therefore are associated with an array of functions in the body. The effects of the vitamins can be categorised into: i) positive effects on the nervous system (B1, B3, B6 and B12); ii) metabolic effects (B1, B2, B3, B5, B6, B7, B8, B9 and B12); iii) haematinic or haematological effects (B6, B9, and B12); and iv) effects on homocysteine levels (B9 and B12) (Schellack et al, 2015; EFSA, 2017).
Fat-soluble vitamins (e.g. vitamins A, D, and E) have to bind to lipids in order to be absorbed by the body. On the other hand, B-complex water-soluble vitamins are readily absorbed from the gastrointestinal tract and only require passage in conjunction with water. These vitamins are not stored in the body in significant quantities, and excess is therefore excreted in the urine (Schellack et al, 2015).
Dietary sources for the B vitamins are various and can be plant-based or animal-based. Consequently, sources include a large range of food products such as meat, vegetables, fish, eggs, potatoes and even whole grain cereals. Not all of these sources contain each B-group vitamin and the composition of each vitamin within them also depends on the food source. For example, vitamin B5 can be obtained from meat, whole grain cereals and broccoli, and vitamin B9 is available in leafy vegetables, legumes, and citrus fruits (Kennedy, 2016). These vitamins are also available – either as the partial or as the whole complex – in beverages, infant milk formula, fortified infant foods, and as dietary supplements. Hypovitaminosis, or vitamin deficiency, can occur in infants, children, and even in adults if they do not consume these vitamins in adequate quantities. There are a variety of symptoms for deficiencies associated to B-group vitamins, for example: vitamin B1 deficiency is associated with general fatigue, gastro-intestinal weakness, and in extreme cases, Beriberi; whereas vitamin B3 deficiency can result in muscle weakness or pellagra with diarrhoea and dermatitis (Kennedy, 2016; WHO/FAO, 2004). As previously stated, the body does not store significant quantities of these vitamins, hence hypervitaminosis (excessive vitamin levels) is very rare.
It is important to keep in mind that vitamins are essential for normal to optimal growth and development. When a well-balanced diet cannot be achieved, vitamin supplementation is recommended in order to avoid states of deficiency that can have a high impact on a growing child. Recommended nutrient intakes (RNIs) and adequate intakes (AIs) for the B-group vitamins during early childhood published by WHO/FAO (2004) and EFSA (2017) are summarised in a table here. These recommended daily dosages can be attained through diet and/or supplementation.back