Lingering fatigue, declining energy, brittle nails, repeated bouts of sluggishness... Behind these subtle signals sometimes lies a deficiency in vitamins or minerals. And contrary to popular belief, deficiencies are not limited to developing countries: they are common also in our societies, despite food abundance.
This guide reviews the most common deficiencies (iron, magnesium, vitamin D, vitamin C, B12), their symptoms and their solutions. And to help you see clearly, we have designed an informative self-test that provides guidance, without ever diagnosing.
The most common deficiencies are iron (the most widespread in the world), vitamin D (very common in winter), magnesium, vitamin B12 (especially among vegetarians) and vitamin C. Their common point: non-specific symptoms, dominated by fatigue. This is why they are not sufficient to make a diagnosis: only a blood test can confirm it. The first solution is a varied diet ; supplementation helps in cases of increased need, particular diet, or confirmed deficiency. Our self-test below points you toward areas to explore with a healthcare professional.
Self-test: which deficiencies to explore?
Deficiencies share many symptoms, which makes self-assessment tricky. This test groups some characteristic signals by nutrient to help you structure the discussion with your doctor. It is in no way a substitute for a blood test.
Self-test: which deficiencies could you explore?
Check the signals you experience. This tool is informational and makes no diagnosis.
Many deficiencies share common signals (fatigue, loss of energy). This orientation test groups some signs by nutrient to help you know which ones to address with a healthcare professional. It does not replace a blood test.
Topics to discuss with a healthcare professional
This result is purely indicative and is not a diagnosis. These signals can have many causes. Only a blood test prescribed by a healthcare professional can confirm a deficiency.
Have you identified one or more areas of concern? Read the corresponding sections below, then discuss them with your doctor, who can prescribe appropriate dosages.
Iron deficiency
It's the champion of deficiencies. According to PubMed, a review by Chaparro and Suchdev 2019 in the Annals of the New York Academy of Sciences reminds us that anemia affects approximately one-third of the world's population, with iron deficiency being one of its main causes (DOI: 10.1111/nyas.14092).
Iron is essential for transporting oxygen in the blood (via hemoglobin). When it's lacking, the body literally runs out of breath. The typical signs : significant fatigue, shortness of breath on exertion, pale complexion, brittle or ridged nails, hair loss, cold hands and feet.
The people most at risk : women of childbearing age (menstrual losses), pregnant women, endurance athletes, vegetarians and vegans (plant-based iron is less well absorbed), and people with digestive disorders. Good news: pairing a source of vitamin C with a meal rich in plant-based iron significantly improves its absorption. To choose wisely, see our comparison on iron forms and our iron bisglycinate, a form renowned for its good digestive tolerance.
Vitamin D deficiency
It's the other major deficiency in our latitudes. Vitamin D is nicknamed the "sunshine vitamin" because our skin synthesizes it through the action of UVB rays. However, from October to April in France, the sun is too low to allow sufficient production: a large portion of the population then has insufficient levels.
Vitamin D contributes to the maintenance of normal bones and muscles and to normal immune system function. According to PubMed, a meta-analysis by Martineau 2017 in the BMJ shows that supplementation reduces the risk of respiratory infections, especially in people with deficiency (DOI: 10.1136/bmj.i6583). The signs : persistent fatigue, diffuse pain, frequent infections, low winter mood. To learn all about it, read our complete guide on vitamin D and discover our plant-based liquid vitamin D3.
Magnesium deficiency
Magnesium is involved in hundreds of reactions in the body, including nerve and muscle function. Chronic stress increases its elimination, and modern diet (refined products) often provides little of it: deficiency is therefore frequent.
Magnesium contributes to normal psychological functions, to normal functioning of the nervous system, and helps reduce fatigue (authorized EFSA claims). The signs of deficiency : cramps, fasciculations (twitching eyelid), muscle tension, irritability, nervousness, poorly managed stress, restless sleep, fatigue upon waking. Stressed, athletic, or elderly individuals are most affected. Discover our Magnesium+ bisglycinate, a well-tolerated and well-absorbed form.
Vitamin B12 deficiency
B12 is a particular case, as it is virtually absent from the plant kingdom : it is found only in meat, fish, eggs, and dairy products. It is the most predictable deficiency, but also the easiest to anticipate.
B12 contributes to normal functioning of the nervous system, to red blood cell formation, and helps reduce fatigue. The signs : intense fatigue, lack of concentration, memory problems, tingling in the hands and feet, sometimes paleness. The at-risk people : vegans and vegetarians (for whom B12 supplementation is not optional but necessary), elderly individuals (reduced absorption), and those with digestive disorders. If you follow a plant-based diet, spirulina and a tailored complex can supplement your diet, but supplemented B12 remains essential: discuss this with your doctor.
Vitamin C deficiency
Vitamin C is water-soluble: the body does not store it, hence the importance of regular intake. Severe deficiency (scurvy) has become rare, but insufficiently low intakes remain possible.
Vitamin C contributes to normal functioning of the immune system, to collagen formation, and helps reduce fatigue. According to PubMed, a 2017 review by Carr and Maggini in Nutrients specifies that intakes of 100 to 200 mg per day optimize immune function (DOI: 10.3390/nu9111211). The signs of deficiency : fatigue, sensitive or bleeding gums, slow wound healing, easy bruising. The smokers have significantly increased needs. To learn more, read our article on natural vitamin C and discover our Organic acerola.
How to prevent and correct deficiencies
Faced with deficiencies, the strategy comes down to three levels, from most to least important.
Food first
It's the foundation. A varied diet (fruits, vegetables, legumes, whole grains, protein sources) covers most needs. Prioritize fresh and minimally processed products, and limit refined foods which reduce magnesium and other mineral intake.
Targeted supplementation when justified
In certain situations, food alone is not enough: vitamin D in winter, B12 in the case of a vegan diet (essential), iron for concerned women or athletes, magnesium during periods of stress. Supplementation is then targeted at the identified deficiency, ideally after blood work.
Multivitamin complex as a safety net
A multivitamin and mineral complex can serve as a safety net to fill in small daily gaps, without replacing healthy eating or targeted treatment for confirmed deficiency. Useful during periods of fatigue, stress, or unbalanced nutrition.
The essential reflex remains the blood test in case of doubt: it prevents both missing a deficiency and supplementing unnecessarily. To support your daily vitality, explore our vitamins and minerals and our selection for fatigue.
Frequently asked questions
What are the most common deficiencies?
The most widespread nutritional deficiencies are iron deficiency (the most common worldwide), vitamin D deficiency (very common in winter at our latitudes), magnesium deficiency, and more specifically, vitamin B12 deficiency (especially among vegetarians and vegans) and vitamin C deficiency. Iodine and calcium deficiencies also exist. These deficiencies often share a common symptom: fatigue.
How do you know if you have a deficiency?
The symptoms of deficiencies (fatigue, loss of energy, various disorders) are nonspecific and overlap. They are therefore insufficient to make a diagnosis. The only reliable way to confirm a deficiency is a blood test prescribed by a healthcare professional, which measures the relevant levels (ferritin for iron, 25-OH vitamin D, etc.). A self-questionnaire can only guide discussion with your doctor.
What are the signs of vitamin deficiency?
The signs of vitamin or mineral deficiency are often diffuse: persistent fatigue, loss of energy, reduced resistance to infections, mood or sleep disorders, brittle nails or hair, cramps, tingling. Since these signals are nonspecific and common to several deficiencies, they should be confirmed by blood work before any targeted supplementation.
Should you take supplements to avoid deficiencies?
The first solution against deficiencies is a varied and balanced diet. Supplementation is useful in certain situations: deficiency confirmed by testing, increased needs (pregnancy, sports), special diet (B12 is essential for a vegan diet), or low sun exposure (vitamin D in winter). A multivitamin complex can serve as a safety net, but it does not replace a healthy diet or medical advice in case of confirmed deficiency.
Which deficiency causes the most fatigue?
Several deficiencies cause fatigue, making diagnosis difficult without testing. The most common culprits are iron deficiency (fatigue, shortness of breath, paleness), vitamin D deficiency (winter fatigue), magnesium deficiency (nervous fatigue, disrupted sleep), and vitamin B12 deficiency (intense fatigue, especially in vegetarians). Only a blood test can identify the precise cause.
Learn more
- Deficiency
- Insufficient intake of a nutrient relative to the body's needs, which may cause health problems. To be distinguished from insufficiency (moderate lack).
- Ferritin
- Iron storage protein, measured in the blood to assess the body's iron reserves.
- Anemia
- Decrease in hemoglobin or red blood cell levels, often caused by iron, B12, or folate deficiency.
- 25-hydroxyvitamin D
- Circulating form of vitamin D measured in the blood to assess status (deficiency below 20 ng/mL).
- Water-soluble / fat-soluble
- A water-soluble vitamin (C, B12) dissolves in water and is not stored; a fat-soluble vitamin (D) is stored in fats.
- Blood test
- Blood analysis prescribed by a health professional, the only reliable method to confirm a deficiency.
- Chaparro CM, Suchdev PS. Anemia epidemiology, pathophysiology, and etiology in low- and middle-income countries. Ann N Y Acad Sci. 2019;1450(1):15-31. doi:10.1111/nyas.14092
- Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections. BMJ. 2017;356:i6583. doi:10.1136/bmj.i6583
- Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. 2017;9(11):1211. doi:10.3390/nu9111211
- ANSES and EFSA. Nutritional references and authorized health claims for iron, magnesium, vitamins D, C, and B12.
About this article. Written by the Nutrition•pro team based on ANSES and EFSA references and peer-reviewed journals indexed on PubMed. This article and its self-assessment are informational and do not replace medical advice. If you experience persistent fatigue or suspect a deficiency, consult a healthcare professional who can order a blood test. Discover our editorial methodology.
