5 things that a nutritionist recommends before starting to take food supplements

A couple in a kitchen with several pills bottles decide which one to take

- Author, Rachel Woods
- Author's title, The Conversation*
August 7, 2025

From collagen powder to gummies for immunity, the supplements are everywhere: in our Instagram messages, on the shelves of the supermarkets and filling the kit of our bathrooms. They are traded as rapid priests against modern greetings, with the promise of giving us better sleep, shiny skin, greater concentration and even longevity.

As a nutritionist, they often ask me if the supplements are worth their cost, and the answer is: it depends. Based on what they claim online, you would believe that they can cure almost everything.

While some supplements do fulfill a valuable role under certain circumstances, they are usually misunderstood and frequently on promoted. However, many people are not aware of the risks, limitations and advertising tricks behind the brands.

Here I propose 5 things that I would like people to know before buying supplements.

1. Start with food, not with supplements

If you can get a nutrient from your diet, that is almost always the best option.

The United Kingdom Food Standards Agency defines a food supplement as a product “intended to correct nutritional deficiencies, maintain adequate intake of certain nutrients, or support specific physiological functions.”

In other words, supplements are there to help your diet, not replace real foods.

Integral foods provide much more than isolated nutrients. For example, fatty fish such as salmon not only provides omega-3 fats, but also protein, vitamin D, selenium or other beneficial compounds. These interact in ways that we do not completely understand and their combined effects are difficult, if not impossible, to replicate with supplements.

A salmon on a tray with tomatoes, herbs and other vegetables, before being baked — Photo foot, Supplements cannot replicate all the benefits of integral foods.

Scientists have tried to isolate the “active ingredients” of fruits and vegetables to recreate their benefits in pills, but without success. The advantages seem to come from the complete food, not a single compound.

That said, there are circumstances in which the supplements are necessary. For example, folic acid is recommended before and after pregnancy to reduce the risk of defects in the fetus neural tubes.

Vitamin D is recommended during the winter months when sunlight is limited. People who follow a vegan diet may need vitamin B12, which is the most found in animal products.

2. You may not realize that you are taking too much

It is much easier to take too much of a supplement than to overcome with food. In the short term, that can generate side effects such as nausea or diarrhea. But in the long term, overconsumum can have severe consequences.

Many people take supplements for years without knowing if they need them or how many are too much. Soluble fat vitamins such as A, D, E and K are stored in the body instead of being excreted.

Too much vitamin D, for example, can produce an accumulation of calcium, which can damage the kidneys and the heart, as well as weaken the bones. High dose of vitamin A can cause damage to the liver, birth defects during pregnancy and a decrease in bone density.

A pregnant woman, stops in front of the shelf of a kitchen takes a pill from a bottle — Photo foot, Pregnant women should pay particular attention to the type of supplement they consume.

Even water soluble vitamins can cause problems, since vitamin B6 vitamin with nerves has been linked.

As most people do not regularly review their blood nutrients levels, many times they don't realize that something is wrong until the symptoms appear.

3. Do not trust the tips on social networks

If you spend a few minutes online you will probably see promoted supplements such as “strengthening of the immune system”, “natural”, or “detoxifiers.” These words may sound convincing, but they have no scientific definition. They are terms of marketing.

The agency that controls advertising standards in the United Kingdom (ASA) has rules about how many health attributions can, including on social networks. But enforcing them is difficult, especially with the marketing of influencers and affiliated programs.

A woman in front of a camera promotes products in jars that holds in her hand — Photo foot, Do not get carried away by online influencers or vendors who have no medical experience.

Marketing strategies known as multilevel marketing (MLM) add more complexity. Sellers, who usually have no medical or scientific training, promote products based on personal anecdotes instead of evidence.

Although ASA provides specific guides of how MLM vendors can promote supplements, these rules are frequently ignored, and rarely imposed and usually drain between regulatory gaps, which results in truly extraordinary powers.

4. The supplement industry is more on sales than science

The global supplement market is valued at more than US $ 100,000 million. Like any great industry, its goals are growth and profits. That influences how products are developed and traded. If a supplement really worked, it would be recommended by doctors, not influencers.

Some supplements are backed with evidence, but these tend to be less striking than others, such as iron or vitamin D.

Many others are publicized with statements that go far beyond what studies demonstrate and are often promoted by people who do not have formal training in nutrition or health care.

Red and pink capsules are distributed to a supplier in a pharmaceutical factory — Photo foot, Nutrition and health supplements trade is a multimillionaire industry.

5. Some supplements are not suitable for all

That they are available without a medical recipe does not mean that a supplement is safe. Even when the products are labeled as “natural” can react with medications or cause damage.

San Juan's grass, sometimes used to lift the spirits, can have dangerous side effects if taken with some antidepressants, contraceptives or drugs for blood pressure.

Vitamin K can interfere with anticoagulants such as warfarin. High dose iron can produce digestive problems and affect how some antibiotics are absorbed.

A pharmacist with a white robe in front of a shelf with pills and medications recommends a woman who is by her side a medication — Photo foot, It is always advisable to request the advice of an expert person.

Many supplements have not been tested in terms of security for pregnant people. It is known that others, such as high dose vitamin A, can be harmful during pregnancy and be transferred through breast milk.

If you are pregnant, breastfeeding, taking medications or dealing with a health condition, talk to a pharmacist, general practitioner or dietitian before starting to take a new supplement.

Supplements can help health when there is a specific need, but they are not a universal remedy. Before spending money on a product that promises a lot, ask yourself this question: do I really need it or would it not be better to spend money on healthy food?

*Rachel Woods is a senior professor at Lincoln University. His original article was published in The Conversation, whose English version you can Read here