Today, the quest for optimal health has led to an exponential increase in the consumption of vitamin and mineral supplements. It is normal that, seeking to boost our energy, strengthen our immune system or prevent disease, we resort to these products. In fact, a recent survey in Spain has revealed that 42% of the population had taken food supplements in the last 12 months, often without professional supervision.
But does this trend represent a real need or an overestimation of their usefulness? As a doctor committed to scientific evidence, analysing this is essential. The unshakeable foundation: balanced diet and healthy lifestyle.
The current scientific evidence is overwhelming: for most healthy, non-pregnant adults, a varied and balanced diet, rich in fruit and vegetables, is sufficient to provide all the essential nutrients the body needs.
Whole foods provide not only vitamins and minerals, but also fibre and other bioactive compounds that supplements cannot replicate and that act synergistically to provide health benefits.
Experts and reputable organisations, such as the United States Preventive Services Task Force (USPSTF), emphasise that the key to staying healthy lies in evidence-based practices such as eating healthy and exercising regularly, rather than relying on “magic pills”. In fact, Americans spent nearly $50 billion on vitamins and dietary supplements in 2021, an expense that, for the healthy population, often represents a waste of money. When benefits are NOT proven in healthy people.
Research has shown a lack of conclusive evidence on the efficacy of supplementation in the prevention of chronic diseases among the general population.
- The USPSTF recommendations note that there is “insufficient evidence” that taking multivitamins, combined or individual supplements, can help prevent CVD and cancer in healthy, non-pregnant adults.
- Beta-carotene supplementation is specifically discouraged because of a possible increased risk of lung cancer, especially in smokers and people exposed to asbestos.
- Vitamin E supplementation has also failed to show any net benefit in reducing the risk of mortality, cardiovascular disease or cancer, and may even increase the risk of haemorrhagic stroke at high doses.
- Other studies conclude that supplementation with folate, vitamins B6, B12, C and D has also shown no benefit in the prevention of CVD or cancer in the general population.
- With regard to omega-3 fatty acids, while consumption of oily fish and seafood is associated with better heart health, it is still unclear whether the benefits come from the omega-3s or from the foods themselves. The American Heart Association (AHA) recommends fish consumption, but not omega-3 supplements for people at high risk of CVD, however it does recommend omega-3 supplements for those with established heart disease, always under medical supervision.
- There is no consistent evidence to support that the use of vitamin D supplements is beneficial for general maintenance of bone health, with the exception of specific conditions such as rickets, osteomalacia and diagnosed osteoporosis.
- A sub-analysis of a study involving more than 25,000 participants found no significant difference in fracture incidence between those taking vitamin D and those receiving placebo.
- The USPSTF considers the evidence for primary fracture prevention with vitamin D supplementation (alone or with calcium) in the general population to be insufficient and, in fact, issues a recommendation against the use of daily doses of less than 400 IU of vitamin D and 1,000 mg of calcium in this context, except in people with a history of osteoporotic fractures or a diagnosis of osteoporosis.
- Vitamin D supplementation has also failed to show a reduction in the risk of falls in healthy, non-institutionalised older adults.
- There is insufficient evidence to support vitamin D administration in the general population to reduce the risk of upper respiratory tract infections, including COVID-19.
- There is also no evidence supporting the role of vitamin E supplementation in the prevention of respiratory infections in older patients.
- Regular supplementation with vitamin C does not reduce the incidence of the common cold.
- There was no difference between vitamin D supplementation and placebo in the incidence or recurrence of depression after 5 years of treatment, studies found.
- The available evidence also does not recommend the use of supplementation with folates, vitamins B6, B12, C, E, beta-carotene and selenium to reduce the risk of cognitive impairment or dementia in the general population.
Although the general healthy population does not usually need supplementation, there are certain groups and situations where the evidence does support its use because, despite not having an evident underlying pathology, they are at risk of deficiency:
- Despite controversy, 25-hydroxyvitamin D determinations in the population are showing widespread deficiency.
- Although routine screening and supplementation are not warranted in the asymptomatic population without risk factors, monitoring and supplementation is nevertheless considered in the institutionalised elderly patients if they present deficiency (< 12 ng/mL), and in these cases it is recommended to combine it with calcium.
- For children and adolescents, supplementation is advised in groups at high risk of vitamin D deficiency (low sun exposure, dark skin) or breastfed infants if their levels are below 10 ng/ml.
- Essential for pregnant women or women trying to become pregnant to prevent neural tube defects (NTDs) in the foetus.
- The general recommendation is a daily intake of 400 mcg from one month before conception and up to 12 weeks gestation.
- In high-risk women (history of NTDs, diabetic, obese with BMI > 35 kg/m², or epileptic women on anticonvulsant treatment), a daily dose of 5 mg is recommended.
- People following a strict vegan or vegetarian diet must unfailingly take supplementation with vitamin B12, as it is not found in plant-based foods.
- Even lacto-ovo vegetarians should consider supplementation.
- The recommended daily dose for individuals over 15 years of age is 4 micrograms. In case of suspected deficiency, higher doses are suggested initially, followed by a maintenance dose
- Although routine supplementation is not recommended for all pregnant women, iron deficiency anaemia is the most common cause of anaemia in this group. Screening is performed and supplementation is given if deficiency is confirmed.
- In children, iron deficiency is the most common nutritional deficiency. Premature or low birth weight infants, as well as those older than 6 months with risk factors, may require iron supplementation.
- Although there are no general recommendations for supplementation in the healthy population, preclinical studies suggest that it may be beneficial in the management of conditions such as chronic kidney disease and metabolic syndrome, where magnesium deficiency is common and aggravates prognosis. However, no trials have been conducted in humans.
It is vital to understand that “more is not always better”. Uncontrolled consumption of supplements, especially of fat-soluble vitamins (A, D, E and K), can be harmful and lead to toxicity or hypervitaminosis. Knowing the tolerable upper intake levels (UL) is crucial to avoid complications.
- Vitamin A (UL: 3.000 mcg for adults): Excess can cause liver damage, nausea, dizziness and, in pregnant women, increased risk of congenital malformations. Intake of beta-carotene, a precursor of vitamin A, has been linked to increased risk of lung cancer in populations at risk.
- Vitamin D (UL: 4,000 IU for individuals > 8 years): Overdose can cause dangerous levels of calcium in the blood (hypercalcaemia), manifesting as anorexia, nausea, vomiting, muscle weakness, cardiac arrhythmias, confusion and, in severe cases, kidney damage and anaemia. High doses (4,000-10,000 IU/day or higher) have also been associated with an increased risk of fractures and/or falls. Chronic toxicity may lead to nephrocalcinosis and bone demineralisation.
- Vitamin E (UL: 300 mg for adults): High doses have been associated with an increased risk of haemorrhagic stroke and, at doses greater than 400 IU/day for more than one year, with an increased risk of death from all causes.
- Iron (Maximum tolerated dose: 45 mg daily for adults): Excess can be toxic, causing gastrointestinal upset (vomiting, abdominal pain, diarrhoea, constipation) and organ damage, especially to the liver. Ingestion of ≥ 60 mg/kg of elemental iron can cause liver injury, shock and death.
- Calcium (UL: 2,500 mg for adults): Consuming more than this amount per day can lead to kidney stones and cardiovascular complications (although the relationship between this and cardiovascular risk is controversial). It may also cause gastric reflux and constipation.
- Magnesium (UL for supplements: 250 mg): Hypermagnesaemia is rare, but can occur in cases of kidney failure or excessive intake. The most common symptoms include diarrhoea, nausea, abdominal pain, decreased tendon reflexes, weakness, paralysis, lethargy, prolonged QT interval, hypotension and respiratory failure.
- Vitamin B12: Whilst it is difficult to consume excess levels that cause harm, as the excess is excreted in the urine and no toxicity has been demonstrated, the determination of its levels in blood can be misleading due to the presence of analogues that increase the value in blood analysis.
A call for moderation and professional consultation
The key to good health does not lie in the amount of vitamins and minerals we consume in the form of supplements, but in the right balance. Although supplementation can be a useful tool in some very specific cases and under medical prescription, it should be done wisely and with caution.
Before starting any supplementation programme, it is essential to consult with a healthcare professional. They can assess your specific nutritional needs, consider your diet, lifestyle, medical history and any medications you are taking, to determine if there is an actual deficiency and determine the best strategy to address it. Prioritising a balanced diet, regular physical activity and a healthy lifestyle remains the strongest foundation for optimising overall wellness and reducing long-term risks.
September 22, 2025
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