Many adults exercise regularly, eat what they believe is a balanced diet and appear perfectly healthy, yet their blood tests may reveal hidden nutritional deficiencies. Vitamin D, iron and vitamin B12 are among the nutrients that can drop below healthy levels without causing obvious physical signs. The only symptoms that you may notice are fatigue, brain fog, hair thinning or even a faster resting heart rate. A lot of these signs are often blamed on stress, poor sleep or a busy lifestyle, and the underlying deficiency goes unnoticed for months or even years.

This is more common than many people realise. A study of apparently healthy urban adults in Hyderabad found that around 46% had low vitamin B12 levels, while nearly 29% were deficient in vitamin D. Another survey found vitamin B12 deficiency in 14% of vegetarian participants, while 82% had low vitamin D3 levels. These findings show that looking fit does not necessarily mean the body is receiving or absorbing all the nutrients it needs.

Why Can Healthy-Looking People Be Deficient?

Dr Vinay Bhat, Associate Director, Internal Medicine, Yashoda Medicity, said that the mismatch between appearance and nutritional status is not unusual. Vitamin D, iron and B12 are involved in several important functions, including oxygen transport, nerve signalling, bone health and immune regulation.

The body can compensate for low levels for some time, prioritising essential functions before symptoms become noticeable. This means a person may continue working, exercising and following their usual routine while a deficiency is gradually developing.

"Many people exercise, eat what they consider a balanced diet, and look healthy. However, their blood test tells a different story," says Dr Bhat.

Modern Lifestyle Can Play A Role

One major reason for vitamin D deficiency is limited exposure to sunlight. People who spend most of their day indoors, particularly those working in offices, may not get enough sunlight for the skin to produce adequate vitamin D. Even people who exercise regularly may spend very little time outdoors during daylight hours.

Diet can also influence iron and B12 levels. Vegetarian diets can sometimes provide less readily absorbable iron and B12, making it important to plan meals carefully. This does not mean that vegetarians will necessarily become deficient, however, they may need to pay closer attention to their intake and, if required, use supplements accordingly.

Certain medicines can also affect nutrient levels. Long-term use of medicines such as metformin and acid-reducing drugs, including proton-pump inhibitors, can interfere with vitamin B12 absorption in some people.

What Are The Early Signs Of Deficiency?

The symptoms of vitamin D, iron and B12 deficiency can overlap, which makes them difficult to identify based on symptoms alone. Common signs may include:

  • Persistent or unexplained tiredness
  • Difficulty concentrating or "brain fog"
  • Mild irritability or changes in mood
  • Hair thinning or increased hair fall
  • Reduced energy during exercise
  • Weakness
  • A faster resting heart rate in some people

Iron deficiency can reduce the body's ability to produce haemoglobin, which carries oxygen in the blood. As deficiency progresses, this can lead to anaemia and symptoms such as fatigue, weakness, breathlessness or paleness.

Vitamin B12 is important for healthy nerves and red blood cells. A prolonged deficiency can cause numbness or tingling, balance problems and neurological symptoms in addition to tiredness.

Vitamin D plays an important role in bone and muscle health and also contributes to normal immune function. Low levels may not cause specific symptoms initially, which is another reason the deficiency can remain hidden.

Who Should Pay More Attention?

Not everyone needs to take supplements or undergo repeated testing. However, testing may be useful for people who have unexplained or persistent fatigue or have factors that increase their risk of deficiency. This includes people who:

  • Follow a vegetarian diet
  • Spend most daylight hours indoors
  • Are above 50 years of age
  • Take metformin for a long period
  • Use proton-pump inhibitors or other acid-reducing medicines for a long time
  • Have symptoms that cannot be explained by sleep, stress or lifestyle
  • Have a diet that is low in nutrient-rich foods

A person's diet and lifestyle should also be considered along with their symptoms and medical history.

Which Tests Can Detect These Deficiencies?

A simple blood test can help identify several common nutritional deficiencies. Dr Bhat recommends considering a baseline panel that includes 25-hydroxyvitamin D, serum vitamin B12, ferritin and a complete blood count (CBC), particularly in people with unexplained fatigue or risk factors.

Ferritin is useful for assessing the body's iron stores, while a CBC can help identify anaemia and other changes in blood cells. Vitamin D and B12 levels can provide further information about whether these nutrients are adequate. However, test results should be interpreted by a doctor rather than used to self-diagnose or self-treat.

Should You Take Supplements Without Testing?

Taking high-dose supplements simply because fatigue or hair fall is present may not always be the right approach. Iron, in particular, should not be taken unnecessarily or in high doses without medical advice, as excess iron can cause other health problems.

The better approach is to identify whether a deficiency actually exists, understand why it has developed and then correct it. Depending on the results, a doctor may recommend dietary changes, supplements or further tests to identify an underlying absorption problem.

Correcting a genuine deficiency can be a relatively simple and cost-effective way to improve health. But supplementation should be based on individual needs rather than assumptions.

"Looking healthy and being nutritionally sufficient are not the same thing. When fatigue lingers without explanation, a basic panel is the only answer," said Dr Bhat.

Disclaimer: This content including advice provides generic information only. It is in no way a substitute for a qualified medical opinion. Always consult a specialist or your own doctor for more information. NDTV does not claim responsibility for this information.