“I’m always tired” is one of the most common health complaints there is — and one of the least specific. Fatigue, brittle nails or frequent colds can come from sleep, stress, illness or diet, and no article can tell you which. What this guide can do is show you which nutrient shortfalls are actually common in the US, what the official intake numbers are, and when the answer is a blood test rather than a bottle.
The honest starting point
Most people eating a varied diet are not deficient in most nutrients. Symptoms alone cannot diagnose a deficiency: tiredness is a symptom of dozens of things, and taking a supplement for a gap you do not have does nothing except cost money. The nutrients below are listed because population surveys keep flagging them, not because everyone needs them.
The shortfalls that actually show up in surveys
Vitamin D
The recommended intake for adults up to 70 is 600 IU (15 mcg) per day, rising to 800 IU after 70. It is genuinely hard to reach from food — oily fish and fortified milk are the main sources — and skin production drops in winter and with sunscreen use, indoor work or darker skin. This is the one nutrient many clinicians check without waiting for symptoms.
Iron
Adult men need 8 mg a day; women aged 19–50 need 18 mg, which is why iron shortfall is far more common before menopause. Real signs are unusual tiredness with pallor or breathlessness on exertion — but iron is also the nutrient where guessing is most dangerous: too much is toxic, and excess iron is a leading cause of poisoning in young children. Iron belongs to a blood test, not a hunch.
Vitamin B12
Adults need 2.4 mcg daily. B12 occurs naturally only in animal foods, so the groups most often short are people eating vegan or largely vegetarian diets, adults over 50 (absorption falls with age) and anyone taking long-term acid-reducing medication.
Calcium
Adults need 1,000 mg a day, rising to 1,200 mg for women over 50 and everyone over 70. People who avoid dairy are the group most likely to fall short, and calcium works together with vitamin D — which is why the two are so often sold in one tablet.
What to do before buying anything
- Write down what you actually eat for a week. Most apparent gaps close with food, and you cannot fix a diet you have not looked at.
- Ask for a blood test. Vitamin D, ferritin (iron stores) and B12 are ordinary, inexpensive tests. A number beats a symptom.
- Then, if there is a gap, supplement the specific nutrient — not a scattergun of everything.
Our companion guide on reading a Supplement Facts label covers how to check the amount you are actually getting per serving.
If a test does point to a gap
These items from our shelf map to the nutrients above: Integrative Therapeutics Iron Complex pairs iron with vitamin C, folate and B12; Integrative Therapeutics Active B-Complex covers the B group including B12; Caltrate Calcium with Vitamin D3 chewables combines the calcium–D pairing described above; and for vitamin D alone, Thorne D-5,000. Talk to your healthcare provider before starting any of them, especially iron.
This article is general information, not medical advice. These statements have not been evaluated by the FDA; supplements are not intended to diagnose, treat, cure or prevent any disease. Intake figures: NIH Office of Dietary Supplements consumer fact sheets for vitamin D, iron, vitamin B12 and calcium.