The science of vitamins and minerals

Key points

• Vitamins and minerals are micronutrients required by the body in small amounts, for a variety of essential processes. Most vitamins and minerals cannot be made by the body, so need to be provided in the diet.
• Requirements for vitamins and minerals vary for different groups according to age, sex, physiological state (such as during pregnancy/lactation), and sometimes due to a person’s state of health.
• The Department of Health has published Dietary Reference Values (DRVs) for vitamins and minerals for different groups of healthy people.
• There is evidence of low intakes of some vitamins and minerals (below the lower reference nutrient intake) in the UK population, although physiological evidence of deficiency occurs in fewer individuals.
• A healthy, balanced diet should provide most of us with a sufficient amount of vitamins (with the exception of vitamin D), minerals and other nutrients needed for good health, without the need for supplements, although supplementation is recommended in some cases.
• The UK government recommends that all children aged between 6 months and 5 years should be given a daily supplement containing vitamins A, C and D.
• Adults and children aged 5 years and over should take (or should be given) a daily 10 microgram (µg) vitamin D supplement during the autumn and winter months.
• Babies from birth to 1 year should be given a daily supplement with 8.5 to 10 micrograms (µg) of vitamin D throughout the year (unless they are consuming more than 500ml of infant formula per day), and children aged 1 to 4 years should be given a daily 10 microgram vitamin D supplement all year round.            
• It is recommended that women who are pregnant, trying to conceive or could become pregnant, take a 400 microgram (µg) folic acid supplement (or a higher dose if recommended by their doctor) daily from pre-conception until 12 weeks of pregnancy.

Summary

Vitamins and minerals are referred to as micronutrients as they are only needed in small amounts by the body (milligram [mg] or microgram [µg] amounts), although they are essential for a diverse range of important physiological functions in the body. The UK government provides a set of dietary reference values (DRVs) for vitamins and minerals, which indicate nutrient requirements according to age, sex, and physiological state (such as during pregnancy and lactation). A healthy, balanced diet should provide enough amounts of vitamins and minerals (with the exception of vitamin D) to meet the needs of most people, although supplementation is recommended in certain situations – for example, children aged 6 months to 5 years should be given a daily supplement containing vitamins A, C and D.

There is evidence of low intakes and/or status of some essential micronutrients among some groups in the population, for example 9% of girls aged 11-18 years meet the criteria for iron deficiency and anaemia. Product labels can provide information on the amount of vitamins and minerals present in a food or drink (although this is not mandatory), and may include health claims describing the relationship between a vitamin or mineral and health, subject to meeting certain criteria.

A vitamin D supplement (10µg/day) is recommended during the autumn and winter months to protect musculoskeletal health. The evidence for a link between low vitamin D status and the risk of acute respiratory tract infections (like flu), and the risk of COVID-19 infection or worse health outcomes, has been reviewed. The Scientific Advisory Committee on Nutrition (SACN) concluded that there may be some added benefit to following existing government advice to obtain a vitamin D intake of 10µg (400IU) per day in reducing the risk of acute respiratory tract infections (ARTIs). A separate report published by the National Institute for Health and Care Excellence (NICE) found that there was not enough evidence to support taking vitamin D solely to prevent or treat COVID-19, although the panel supported existing government advice for everyone to take a vitamin D supplement (10µg/day) during the autumn and winter months to support bone and muscle health.

Well-planned vegetarian and vegan diets can be suitable for all life stages, although micronutrients typically provided by foods of animal origin in the UK diet, such as vitamin B12, calcium, iron and iodine, should be given special consideration to ensure adequate intakes (especially for vulnerable groups such as pregnant women and infants).

What are vitamins and minerals, and why are they important?

Vitamins and minerals are classified as micronutrients, because they are normally required only in small amounts by the body (typically milligram [mg] or microgram [μg] amounts), although they are essential for a variety of physiological processes and functions, including

• essential constituents of body tissues (such as calcium in bone) and fluids (such as sodium, calcium and potassium)
• components of enzymes (such as zinc) or enzyme co-factors (such as vitamin B12) involved in a diverse range of processes
• antioxidants that prevent damage from free radicals (such as vitamins E and C)
• pro-hormone (only vitamin D)

Vitamins are often grouped into two categories - water-soluble (including vitamin C) and fat-soluble (including vitamin E). Most vitamins cannot be synthesised by the body and so must be obtained by the diet, although vitamin D can be synthesised by the action of sunlight on the skin. Small amounts of niacin (also known as vitamin B3) the amino acid tryptophan (at an approximate ratio of 60mg of tryptophan for 1mg of niacin).

Clinical deficiencies can result in mild to life-threatening symptoms. Some examples of micronutrient deficiencies include:

• Scurvy: Severe vitamin C deficiency, with symptoms including swollen, bleeding gums (teeth can fall out), severe joint or leg pain and skin that bruises easily.
• Rickets (children) or osteomalacia (adults): A lack of vitamin D and/or calcium that can lead to poor bone growth and development, including weak bones that can become deformed.
• Goitre: A swelling of the thyroid gland in the neck, which may occur due to a lack of iodine in the diet (although there are other potential causes).

While these conditions are rare in the UK, micronutrient deficiencies are widespread globally and represent a significant public health concern. For example, a lack of iron, folate and vitamins B12 and A can lead to anaemia, a condition which affects an estimated 42% of children under 5 years of age and 40% of pregnant women worldwide and can lead to difficulties in ability to work or in educational attainment. Vitamin A deficiency is considered the leading cause of preventable blindness in children globally and can increase the risk of disease and death from severe infections (such as diarrhoea and measles).  

Vitamins and minerals in a healthy diet (intakes and recommendations)

In the UK, we have a set of dietary reference values (DRVs) for vitamins and minerals, which provide estimates of the physiological requirements for different groups of healthy people within the population. However, these are not intended to be recommendations or goals for individuals. The European Food Safety Authority (EFSA) has also published a series of scientific opinions on DRVs for vitamins and minerals, as well as a DRV finder tool for use by those working in nutrition. Take a look at the DRV finder tool on EFSA’s website.

There are four types of DRV in the UK:

• Estimated Average Requirements (EARs): The EAR is an estimate of the average requirement of a nutrient needed by a group of people, that is approximately 50% of people will require less, and 50% will require more.
• Reference nutrient intakes (RNIs): The RNI is the amount of a nutrient that is enough to ensure that the needs of nearly all a group (97.5%) are being met.
• Lower reference nutrient intakes (LRNIs): The LRNI is the amount of a nutrient that is enough for only a small number of people in a group (2.5%) who have low requirements, that is, the majority need more.
• Safe Intake: The Safe Intake is used where there is insufficient evidence to set an EAR, RNI or LRNI. The Safe Intake is the amount judged to be enough for almost everyone, but below a level that could have undesirable effects.

More information on micronutrient requirements for different age and sex groups can be found in the Nutrition Requirements resource below.

Most DRVs for vitamins and minerals are given as the RNI, except for the vitamin D intake of children under 5 years, for whom a Safe Intake is recommended.

Data on the proportion of individuals in UK from each age group that are not achieving the LRNI is provided by the National Diet and Nutrition Survey (NDNS); a continuous cross-sectional survey, which provides nationally representative data on the food consumption, nutrient intake and nutritional status of the general population aged 1.5 years and over. This provides an indication of micronutrients of concern, for which there is evidence of inadequate intakes. For example, if 10% of a population group have intakes of a nutrient below the LRNI, it is highly likely that most of these people are having insufficient amounts for their needs.

Survey data from NDNS indicates that average intakes of several vitamins and minerals are low among some groups in the UK population (see Table 1), especially among adolescent girls aged 11-18 years (Table 1). However, there is uncertainty around the clinical relevance of low intakes of some micronutrients (such as magnesium, potassium, selenium), as their respective DRVs were set in 1991, and were based on limited scientific data.

Table 1. Prevalence of micronutrient intakes (excluding supplements) below the lower reference nutrient intake (LRNI) for some vitamins and minerals of concern in the UK population

 Note: The LRNI is the amount that is considered sufficient for only 2.5% of the population with the lowest physiological requirements. Source: National Diet and Nutrition Survey Years 9 to 11 (2016/17 to 2018/19).

There is also evidence of inadequate status or deficiency for some essential micronutrients, including iron and vitamin D (Table 2). For example, 9% of girls aged 11-18 years meet the criteria for iron deficiency and anaemia.

Table 2. Percentage of UK population with low status for some micronutrients

^aMean 25-hydroxyvitamin D status below 25 nmol/L indicating increased risk of deficiency; ^bHaemoglobin and plasma ferritin concentrations below the World Health Organization (WHO) age/sex dependent thresholds for iron deficiency and anaemia; ^cPercentage with red blood cell folate concentrations below the clinical threshold for deficiency (305 nmol/L), or the threshold for increased risk of neural tube defects for women of childbearing age (748 nmol/L);^dFigures in square brackets indicate a sample size less than 50.

High intakes of some micronutrients over time may lead to the risk of toxicity. Maximum recommended safe limits have been published for both the UK (safe upper levels) and the EU (tolerable upper intake levels) to provide guidance on the maximum level of long-term intake of vitamins and minerals that is unlikely to pose a risk of adverse health outcomes.

Labelling of vitamins and minerals

The back-of-pack nutrition information provided on food labels sometimes indicates the amount of vitamins and minerals that a product contains as a percentage of the reference intake (RI), as outlined in European law, although it is not mandatory to provide this information. Other than in Northern Ireland, European regulations governing the legal requirements for the labelling of foods will continue to apply following the UK’s departure from the EU. For more information read the FSA's article on packaging and labelling.

Several health claims relating to specific vitamins and minerals have been authorised for use on products sold in Great Britain (England, Scotland and Wales). Health claims provide information about the relationship between intake of a vitamin, mineral (or other food component) and health. For example, ‘Calcium is needed for the maintenance of normal bones.’ The use of health claims on product labels typically requires that a product provides at least a ‘source of’ a vitamin or mineral (15% of the RI per 100g or 100ml, or 7.5% per 100ml for beverages), although other specific conditions may apply for use to be permitted.

Vitamin and mineral supplements

There are some cases in which supplementation is recommended :

• The UK government recommends that all children aged between 6 months and 5 years should be given a daily supplement containing vitamins A, C and D.
• Adults and children aged 5 years and above should take (or should be given) a daily 10 microgram (µg) vitamin D supplement during the autumn and winter months.
• Babies from birth to 1 year should be given a daily supplement with 8.5 to 10 micrograms (µg) of vitamin D throughout the year (unless they are consuming more than 500ml of infant formula per day), and children aged 1 to 4 years should be given a daily 10 microgram vitamin D supplement all year round.
• The government recommends that people who are not able to go outside often, or who cover their skin while outside, should take a daily 10 microgram (µg) vitamin D supplement all year round.
• People with dark skin, including those from and African, African-Caribbean or South Asian background, should consider take a daily 10 microgram (µg) vitamin D supplement all year round
• It is recommended that women who are pregnant, trying to conceive or could become pregnant, take a 400 microgram (µg) folic acid supplement daily from preconception until 12 weeks of pregnancy. This is to reduce the risk of the baby being born with a neural tube defect.

Aside from these specific instances in which supplementation is recommended, however, eating a balanced and varied diet should provide sufficient amounts of the vitamins, minerals and other nutrients that are needed, as well as important dietary components such as fibre and natural bioactive compounds (such as polyphenols). It is important to remember that supplements should not be used as a substitute for a healthy diet.

Several reviews and meta-analyses (where data from a number of studies are analysed together) have generally shown there to be no beneficial effects of vitamin and mineral supplements for reducing the risk of chronic diseases (such as cancer and cardiovascular disease). In some cases, the use of high dose supplements (such as beta-carotene) has been shown to have adverse effects on disease risk.

For individuals who are worried that they may not be getting enough vitamins and minerals from their diet  (other than those recommended by government), it is a good idea speak to a doctor or another healthcare professional (such as a dietitian or pharmacist), who will be able to advise on whether it is necessary for their specific needs or health status, and any issues to be aware of (including interactions with prescribed medications). If using vitamin or mineral supplements, it is a good idea to buy from a reputable company, such as a local pharmacy, supermarket or a high street retailer, to ensure that the product meets the UK requirements for safety (see above). It is also important to always read the label and make sure not to exceed the recommended dosage.

More information is available in our Food Supplements factsheet below.

Is there a link between vitamin D and COVID-19? What about other respiratory tract infections?

There is evidence from population studies and supplementation trials to suggest that an adequate vitamin D status may be protective against acute respiratory tract infections (ARTIs), such as the common cold and flu, although it is unclear whether there is a causal link between the two.

The emergence of the COVID-19 pandemic in 2020 prompted an increased public interest in a potential association between low vitamin D status and an increased risk of COVID-19, or worse health outcomes linked to COVID-19 (including increased risk of hospitalisation). In response, rapid evidence reviews were published in June 2020 by SACN and the National Institute for Health and Care Excellence (NICE), with support from Public Health England (PHE), assessing the evidence for a link between vitamin D status and/or supplementation and the risk of COVID-19 or ARTIs. Due to continued interest in the potential association between vitamin D status and COVID-19, the Secretary of State for Health and Social Care requested a further review of the evidence on vitamin D and COVID-19, and updated evidence reviews were published in December 2020.

They reached the following conclusions:

For more information read our article on COVID-19 and vitamin D supplements.

Can vitamin C prevent the common cold?

Vitamin C has been proposed for treating respiratory infections since it was first isolated in the 1930s. It became particularly popular in the 1970s, when Nobel laureate Linus Pauling concluded from earlier placebo-controlled trials that vitamin C would prevent and alleviate the common cold.  More recently, a systematic Cochrane review, which only included placebo-controlled trials testing 200mg/day or more of vitamin C (an amount that can easily be consumed as part of a balanced diet), found that regular ingestion of vitamin C had no effect on the incidence of the common cold in an ordinary population. In the same analysis, regular supplementation did lead to a modest reduction in the duration and severity of symptoms, although this level of benefit does not seem to justify long-term vitamin C supplementation in its own right.

There is evidence from trials including marathon runners and skiers to suggest that for people exposed to brief periods of severe physical exercise and/or cold environments, a regular vitamin C intake above 200mg/day approximately halves the risk of the common cold, although caution should be taken in generalising these findings to the broader population. Trials in which high doses of vitamin C were administered therapeutically, after the onset of symptoms, do not show any consistent positive effect on the duration or severity of symptoms. Therefore, while getting enough vitamin C from a healthy and balanced diet is important (adults need 40mg/day), taking large doses to treat or prevent the common cold is unlikely to have a significant benefit and the body will excrete any excess vitamin C that is not needed in the urine.

Do vegetarian and vegan diets provide enough vitamins and minerals? Is it necessary to take a supplement?

Although only about 3% of the UK population report following a vegetarian diet, with about 1% following a vegan diet, interest in eating a more ‘plant-based’ diet has increased in recent years. Well-planned vegetarian and vegan diets can support good health at all ages and life stages, although there are some nutrients that require more consideration if restricting or eliminating animal-based foods from the diet, especially for vulnerable groups such as young children and pregnant women. Important nutrients to consider include:

• Vitamin B12: Only naturally occurring in foods of animal origin, such as meat, fish, eggs and milk. Vegans should include foods fortified with vitamin B12 in their diet (such as fortified breakfast cereals) but may wish to consider a vitamin B12 supplement to ensure an adequate intake. However, they should speak to a GP or other health professional before beginning to take supplements.
• Iron: Plant-based sources of iron, such as beans, lentils, nuts and green vegetables, provide ‘non-haem’ iron that is less bioavailable than the ‘haem’ iron provided by meat. Including a source of vitamin C with meals, such as glass of orange juice, citrus fruits or peppers, can increase the absorption of non-haem iron from the diet.
• Calcium: Vegans can obtain calcium from fortified dairy alternatives, dried fruits, some green leafy vegetables (such as kale and watercress), bread and calcium-set tofu.
• Iodine: Milk and milk products are the main provider of iodine in the UK diet. Iodine can be found in plant foods, such as wholegrains, although the amount varies depending on the levels in the soil where the plants were grown. Some plant-based milk alternatives (such as oat and soya drinks) are fortified with iodine, but it is important to check the label to make sure.
• Vitamin D: Plant-based sources of vitamin D include fortified foods, such as some vegetable spreads, breakfast cereals and plant-based dairy alternatives (check the label), as well as UV-irradiated mushrooms. Most vitamin D supplements contain vitamin D₃, which is typically derived from a wax called lanolin extracted from sheep’s wool, and so may not be suitable for vegans, although vitamin D3 supplements made from lichen are available.

The bioavailability of plant-based sources of minerals also needs to be considered in planning a vegetarian or vegan style diet. For example, phytates found in plant foods such as wholegrains and beans can reduce the absorption of some minerals, including iron, zinc and calcium. Iodine absorption may be hindered by nitrates and, similarly, oxalate present in spinach and rhubarb binds any calcium present, making it unavailable for absorption. The way in which plant foods are processed and prepared for eating can, however, increase the absorption of minerals. This includes soaking and then rinsing dried beans before cooking to increase iron absorption, or the fermentation of grains prior to cooking, which can reduce the phytate content. Although the bioavailability of some micronutrients may be lower from plant-derived foods, NDNS data provides evidence of low intakes (below the LRNI) in the UK population irrespective of diet (see above), highlighting the importance of dietary quality and diversity whether following an omnivorous, vegetarian or vegan diet.

Last reviewed June 2021. Next review due June 2024.