Vitamin and mineral supplements: when are they needed?

What is a food supplement, and what is required for it to be sold in Spain?

A food supplement is a food containing concentrated nutrients or other substances, presented in small doses. It may come as capsules, drops or powder. In Spain, its sale must be notified and it must comply with rules on composition, labelling and safety [1].

Notification does not mean that the product has been shown to improve the health of the person buying it. Health claims must be authorised. The packaging cannot present it as a treatment for a disease [1]. Before deciding, you can consult AESAN’s search tool and guidance.

B12, folic acid, iodine, vitamin D and iron, one by one

The indication depends on the person and the nutrient. These situations call for different decisions; none justifies taking a random multivitamin.

• On a vegan diet, a B12 supplement is essential and should be prescribed by your doctor or registered dietitian-nutritionist; it is also often needed if you eat eggs or dairy [2]. This is explained in the vegetarian eating guide and the guide to common mistakes in vegetarian diets.
• Before and early in pregnancy, folic acid reduces the risk of neural tube defects. Your midwife or doctor decides on the plan [3]. Review the folic acid guide with your midwife.
• During pregnancy and breastfeeding, requirements for iodine increase; your midwife or doctor will assess whether a supplement is needed based on your diet and thyroid context [4]. More details are in the pregnancy eating guide.
• Vitamin D may require supplementation in specific situations, but one test result alone does not determine the dose [5]. Read the vitamin D guide.
• If a blood test confirms iron-deficiency anaemia, your doctor investigates the cause and decides on replacement [6]. The anaemia guide explains how diet can help.

Why doesn’t a multivitamin make up for an incomplete diet?

A multivitamin provides isolated nutrients in defined amounts. It does not provide the variety of foods, fibre and sufficient meals that support an eating pattern. Nor does it address the cause of persistent tiredness.

The review of large trials used by the US prevention task force found insufficient evidence to recommend multivitamins to prevent cancer or cardiovascular disease in healthy adults [7]. That conclusion does not apply to someone with a deficiency, who is pregnant or living with a chronic disease. In those situations, the specific nutrient is assessed.

Before adding a capsule, work out which specific need you want to address.

In everyday meals, pulses with vegetables and a piece of fruit address needs that the packaging cannot describe. If your schedule makes it hard to eat enough, we first work on a practical eating plan. When a supplement is appropriate, it has a specific goal and follow-up.

What are the risks of taking several supplements at once?

Excess can easily occur when two products contain the same nutrient. Fat-soluble vitamins, such as vitamins A and D, can build up. Too much vitamin D can raise calcium levels and damage the kidneys [5]. During pregnancy, high amounts of preformed vitamin A require particular caution [8].

To compare labels, it helps to know the daily upper limit, which includes fortified foods and supplements. It is not a target dose [9]. See “Breastfeeding supplements”.

Safe upper limits for vitamin D and added folate vary by age and are not recommended doses [9]. If you take several products, ask a professional to review the total amount. For children, follow the paediatrician’s instructions.

Some supplements interact with medicines: coenzyme Q10 may interfere with warfarin and insulin [10]. Before taking it, consult your doctor or pharmacist and do not change your treatment on your own. Avoid products from unknown sources that promise weight loss [11].

Do antioxidant supplements work?

Antioxidants are not a treatment category. Eating fruit, vegetables, pulses and nuts contributes to a varied diet; a concentrated extract does not by itself reproduce that pattern.

The US prevention task force advises against beta-carotene and vitamin E supplements to prevent cancer or cardiovascular disease in adults without deficiencies [7]. With beta-carotene, harm was observed especially in people who smoked or were exposed to asbestos. We do not extend that recommendation to ordinary foods.

The body produces coenzyme Q10. Overall evidence does not support using it to relieve statin-associated muscle pain [10]. For cardiovascular prevention and other uses, the results are uncertain. If tiredness is the reason, our chronic fatigue guide explains how persistent symptoms are assessed.

If you are concerned about symptoms while taking a statin, consult the person who prescribed it before making any changes. Our fibromyalgia guide also addresses questions about magnesium, vitamin D and coenzyme Q10.

What mistakes do we see in consultations?

We see people who mistake a low figure for an automatic prescription. A result needs context: symptoms, medical history, medicines and the reason the test was ordered. We also see labels with striking percentages but no defined need.

Another common question is whether “natural” means safe. Source, amount and interactions still matter. If a product promises to treat several things at once, ask for a clear explanation of the expected result and how it will be checked.

How do we decide with you whether it is worth taking?

First, we ask a specific question: which nutrient might be lacking, and why? We review your eating plan, fortified foods, available test results and symptoms. If a deficiency or disease needs investigating, we coordinate medical assessment. The aim is to agree what to measure and when to review the result.

Then we compare the total intake with the needs for your age and situation. In childhood, pregnancy, breastfeeding or kidney disease, this review requires particular care .

We also distinguish between correcting a deficiency and seeking general prevention. These are different questions, and evidence for one does not answer the other. If the reason is “to have more energy”, we first look at sleep, adequate food intake and possible medical causes.

Which myths should be dismissed?

“A higher amount works better” is a poor way to choose a product. An upper limit is the maximum amount considered safe in the long term, and exceeding it can cause harm [9]. Nor are all excess vitamins simply eliminated in the urine: fat-soluble vitamins deserve particular attention.

“If it is sold, its effectiveness has been proven” confuses marketing requirements with a clinical result. Notification and labelling rules do not prove that it will help you [1]. The same applies to collagen and anti-ageing products, which we discuss in our longevity guide. And “if I take a capsule, I eat well” overlooks that food provides more than isolated vitamins.