Nutrient deficiencies: common signs, risks, tests, and fixes

TL;DR:

• Iron, vitamin D, iodine, vitamin A, and zinc are common gaps.
  
• Fatigue, hair loss, poor night vision, and brittle nails are red flags.
  
• Pregnant women, young kids, older adults, and vegans face higher risk.
  
• Confirm with lab tests, then correct with diet, fortified foods, or supplements.
  
• Recheck levels and watch for interactions with medicines.
  

What counts as a nutrient deficiency

A deficiency means your body does not have enough of a vitamin or mineral to work well. Mild gaps can cause subtle symptoms. Severe ones can damage vision, bones, thyroid function, immunity, and growth. The World Health Organization calls iron, vitamin A, and iodine shortfalls the most common worldwide.

The big five: where gaps often show up

1) Iron

What it does. Iron helps carry oxygen in your blood.
Signs of low levels. Tiredness, shortness of breath on effort, pale skin, headaches, brittle nails, and poor focus. With anemia you may feel dizzy and cold. NIH notes effects on cognition and immunity.
Who is at risk. Menstruating people, pregnant women, toddlers, teens, frequent blood donors, those with gut disorders, and people on very low meat diets.
How to test. Ask for a complete blood count, ferritin, and sometimes transferrin saturation.
Food fixes. Red meat, poultry, seafood, beans, lentils, tofu, spinach, pumpkin seeds, and iron-fortified cereals. Pair plant iron with vitamin C foods like citrus or peppers to boost absorption.
When to supplement. If ferritin is low or you have anemia confirmed by tests. Work with a clinician to set dose and duration.

2) Vitamin D

What it does. Vitamin D aids calcium absorption and supports bones and immunity.
Signs of low levels. Bone pain, frequent infections, muscle weakness, and in children, rickets.
Who is at risk. People with little sun exposure, darker skin, older adults, those with obesity, and people with fat-malabsorption.
How to test. Serum 25-hydroxyvitamin D.
Food fixes. Fatty fish, egg yolks, fortified milk and plant milks.
When to supplement. If levels are low on a blood test. Global research suggests deficiency is common, though definitions vary. A 2023 meta-analysis estimated 15.7 percent had very low levels under 30 nmol/L.

3) Iodine

What it does. Iodine is vital for thyroid hormones, which control growth, energy use, and brain development.
Signs of low levels. Goiter, fatigue, feeling cold, weight gain, and in pregnancy, risk to the baby’s brain development.
Who is at risk. People who avoid iodized salt, live in areas with iodine-poor soil, or eat a lot of goitrogenic foods without iodine balance.
How to test. Population surveys use urinary iodine. For individuals, doctors may assess thyroid function and diet.
Food fixes. Iodized salt, seafood, dairy, and eggs.
Population progress. UNICEF estimates about 89 percent of people consume iodized salt, yet gaps persist in some regions.

4) Vitamin A

What it does. Supports vision, skin, and immune defenses.
Signs of low levels. Night blindness, dry eyes, and in severe cases, corneal damage. Xerophthalmia and Bitot spots can appear with advanced deficiency.
Who is at risk. Children and pregnant women in areas with low dietary variety, and people with fat-malabsorption.
Food fixes. Liver, dairy, eggs, and carotenoid-rich produce like carrots, sweet potatoes, mangoes, and dark leafy greens.

5) Zinc

What it does. Helps immune function, wound healing, taste, and smell.
Signs of low levels. Slow wound healing, frequent infections, taste or smell changes, hair loss, and poor appetite.
Who is at risk. People with gut disease, alcohol use disorder, restricted diets, or chronic diarrhea.
Food fixes. Meat, shellfish, beans, nuts, seeds, and whole grains.

Hidden hunger vs. clinical deficiency

You can meet calorie needs yet fall short on key micronutrients. This is called hidden hunger. Large studies suggest billions do not get enough essential micronutrients from diet alone, including calcium, iron, and vitamins C and E. A 2024 analysis estimated widespread inadequate intakes for many nutrients.

Who faces higher risk

• Pregnancy and breastfeeding. Higher needs for iron, iodine, folate, and others.
  
• Infants, children, and teens. Rapid growth increases risk of iron, vitamin A, iodine, and zinc gaps. WHO estimates anemia remains common in young children and women of reproductive age.
  
• Older adults. Lower appetite, less sun exposure, and absorption issues raise risk for vitamin D, B12, and iron shortfalls.
  
• People with restricted diets. Vegans and vegetarians must plan for iron, B12, iodine, zinc, calcium, and omega-3s.
  
• Chronic conditions. Celiac disease, inflammatory bowel disease, bariatric surgery, kidney disease, and diabetes can affect levels.
  
• Certain medicines. Metformin can lower B12. Proton pump inhibitors can lower magnesium and B12 over time. Check interactions with your clinician.
  

Symptoms you should not ignore

Fatigue is common but easy to miss as a warning sign. Look also for shortness of breath on effort, brittle or spoon-shaped nails, hair loss, poor wound healing, frequent infections, mouth cracks, numbness or tingling, bone pain, and night vision problems. These signs overlap across nutrients, so testing matters before you supplement.

How to confirm a deficiency

Step 1: Review risks and symptoms

Note diet patterns, medical conditions, medicines, and family history.

Step 2: Get targeted lab tests

• Iron status. CBC, ferritin, sometimes transferrin saturation.
  
• Vitamin D. 25-hydroxyvitamin D.
  
• Iodine and thyroid. TSH, free T4, and diet review.
  
• Vitamin B12 and folate. Serum B12, MMA or homocysteine if needed.
  
• Zinc. Serum zinc, interpreted with clinical context.
  Testing helps you avoid guessing and avoid excess dosing.
  

Step 3: Search for causes

Low intake is one cause. Others include heavy periods, pregnancy, frequent blood donation, chronic infections, malabsorption, and food insecurity. In anemia, dietary iron deficiency is a leading global cause of lost healthy life years.

Fixing common deficiencies safely

Food first

Start with diet. Whole foods deliver nutrient packages, fiber, and phytonutrients that pills cannot match.

High-yield swaps

• Choose iron-fortified breakfast cereal, add berries or citrus to aid absorption.
  
• Swap refined grains for whole grains to raise magnesium and B vitamins.
  
• Add a weekly oily fish meal for vitamin D and omega-3s.
  
• Use iodized salt in home cooking if safe for your blood pressure.
  
• Include a handful of nuts or seeds for zinc and vitamin E.
  
• Add dark leafy greens and orange vegetables for carotenoids.
  

Fortified foods

Fortified milks, plant milks, cereals, and salt help close gaps at low cost. Many countries use salt iodization to prevent deficiency. Still, quality and coverage can vary, and some populations remain unprotected.

Supplements, with a plan

Use supplements when tests show a deficiency or your clinician advises them due to higher needs.

Iron

• Forms like ferrous sulfate or ferrous bisglycinate are common.
  
• Take on an empty stomach if you can, or with vitamin C.
  
• Avoid tea and coffee near dosing.
  
• Alternate-day dosing can reduce stomach upset in some people.
  
• Keep iron away from children. Iron overdose is dangerous.
  

Vitamin D

• D3 is common. Dose depends on your level, weight, and sun exposure.
  
• Recheck in 8 to 12 weeks after starting a new dose.
  

Iodine

• Pregnant and breastfeeding people often need more. Many prenatal vitamins include iodine.
  
• Do not megadose. Too much iodine can harm thyroid function.
  

Zinc

• Short courses can correct low levels.
  
• High zinc can lower copper. Avoid long high-dose use without medical oversight.
  

Multivitamins

• Can help fill small gaps, but they vary. Choose a product that matches age, sex, and life stage. Avoid high doses you do not need.
  

Interactions and safety checks

• Iron competes with calcium for absorption. Separate doses if both are needed.
  
• Zinc can lower copper with high, prolonged doses.
  
• Vitamin K interacts with warfarin. Keep intake steady, not zero.
  
• Some supplements change lab results. Tell your clinician what you take.
  
• Store supplements out of children’s reach.
  

A quick checklist

Sample 1-day plate to cover bases

• Breakfast. Fortified whole-grain cereal with milk or fortified soy milk, sliced kiwi.
  
• Lunch. Lentil and spinach salad with bell peppers and olive oil, whole-grain pita, yogurt.
  
• Snack. A small handful of mixed nuts and seeds.
  
• Dinner. Baked salmon or fortified tofu, roasted sweet potato, steamed broccoli, brown rice.
  
• Seasoning. Use iodized salt in cooking if advised by your clinician.
  

When to see a clinician now

Seek care if you have chest pain, fainting, severe shortness of breath, very pale skin, or vision changes. These may signal severe anemia or vitamin A problems and need prompt evaluation.

Why it matters

Nutrient shortfalls sap energy, slow learning, and strain health systems. Iron deficiency alone drives large losses in healthy life years. Many gaps are preventable with better diets, sensible fortification, and smart screening for those at risk.

Sources:

• World Health Organization, Micronutrients overview, https://www.who.int/health-topics/micronutrients, accessed 2025-09-30
  
• World Health Organization, Anaemia fact sheet, https://www.who.int/news-room/fact-sheets/detail/anaemia, updated 2025-02-10
  
• UNICEF Data, Iodine, https://data.unicef.org/topic/nutrition/iodine/, updated 2023-03-02
  
• NIH Office of Dietary Supplements, Iron Fact Sheet for Health Professionals, https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/, updated 2025-09-04
  
• Cui A et al., Global and regional prevalence of vitamin D deficiency in population-based studies, 2000–2022, Frontiers in Nutrition, 2023, https://pmc.ncbi.nlm.nih.gov/articles/PMC10064807/
  
• Kiani AK et al., Main nutritional deficiencies, 2022, https://pmc.ncbi.nlm.nih.gov/articles/PMC9710417/
  
• Passarelli S et al., Global estimation of dietary micronutrient inadequacies, The Lancet Global Health, 2024, https://www.thelancet.com/journals/langlo/article/PIIS2214-109X%2824%2900276-6/fulltext
  
• GBD 2021 Anaemia Collaborators, Global anemia burden, The Lancet, 2023, https://pubmed.ncbi.nlm.nih.gov/37536353/