Can Vitamin Supplements Make You Feel Tired?

Curated by Claudia Shannon / Research Scientist / ishonest


Taking recommended amounts of vitamins won't cause fatigue. Excessive doses may cause fatigue and other side effects.

Safe Vitamin Use

There's no consensus on whether or not vitamin supplements offer any benefit for your health. But one thing experts can agree on is that taking too much of certain nutrients can be risky. That's why the Food and Nutrition Board of the National Academies of Medicine has developed recommendations both for daily intakes and limits.

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The recommended dietary intake (RDI) is the total amount of a nutrient — from both food and supplements — deemed safe, necessary and adequate for promoting optimal health in the general population. Some of these amounts differ for men and women. The RDIs for men are:

  • Vitamin A: 900 micrograms
  • Vitamin C: 90 milligrams
  • Vitamin D: 15 micrograms
  • Vitamin E: 15 milligrams
  • Vitamin K: 120 micrograms
  • Thiamin: 1.2 milligrams
  • Riboflavin: 1.3 milligrams
  • Niacin: 16 milligrams
  • Vitamin B6: 1.3 milligrams
  • Folate: 400 micrograms
  • Vitamin B12: 2.4 micrograms
  • Pantothenic acid: 5 milligrams
  • Biotin: 30 micrograms

For women, the RDIs are:

  • Vitamin A: 700 micrograms
  • Vitamin C: 75 milligrams
  • Vitamin D: 15 micrograms
  • Vitamin E: 15 milligrams
  • Vitamin K: 90 micrograms
  • Thiamin: 1.1 milligrams
  • Riboflavin: 1.1 milligrams
  • Niacin: 14 milligrams
  • Vitamin B6: 1.3 milligrams
  • Folate: 400 micrograms
  • Vitamin B12: 2.4 micrograms
  • Pantothenic acid: 5 milligrams
  • Biotin: 30 micrograms

Excess Vitamin Intake

Taking high doses of vitamins without your doctor's recommendation puts you at risk of side effects that can be not only uncomfortable but also life- threatening. Fatigue is one of the more mild symptoms of vitamin overdose, but it's still disruptive to optimal daily functioning and counter to the reasons most people take vitamins in the first place.

Vitamin Overdose and Fatigue

Any vitamin, when taken in excess, has the potential to cause fatigue and result in numerous other adverse effects. But for a few vitamins, it's a documented side effect.

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Niacin: When taken in doses over 1,000 milligrams per day, niacin can cause fatigue, warns National Institutes of Health. Other symptoms include low blood pressure and an associated risk of falls, nausea, heartburn and abdominal pain, impaired glucose tolerance and insulin resistance, and effects on the eyes such as blurred vision or macular edema, in which fluid builds up in the retina.

Vitamin E: According to the Mayo Clinic, doses greater than 400 international units (IU) daily can cause unusual fatigue and weakness, as well as headaches, diarrhea, blurred vision, dizziness and nausea or stomach cramps.

Folate: Excess intake of folate, on its own, isn't likely to cause fatigue. But, according to NIH, taking too much folate can mask a deficiency in B12, one of the main symptoms of which is fatigue. It can also exacerbate the symptoms associated with B12 deficiency.

How Much Can You Take?

To prevent fatigue from vitamin supplements, it's important to stay below the recommended upper intake levels (UL) from the Food and Nutrition Board. Consuming less than these amounts is considered to be safe for the general population.

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Some nutrients don't have a UL because even very high doses are believed to not pose a risk for healthy people. These mainly include the water-soluble B vitamins, which your body doesn't store; excess is excreted in your urine and stool, and you must replace them each day. But as noted above, you should take caution with folate and biotin.

The ULs for the 13 vitamins are the same for men and women and are as follows:

  • Vitamin A: 3,000 micrograms
  • Vitamin C: 2,000 milligrams
  • Vitamin D: 100 micrograms
  • Vitamin E: 1,000 milligrams
  • Vitamin K: No UL
  • Thiamin: No UL
  • Riboflavin: No UL
  • Niacin: 35 milligrams
  • Vitamin B6: 100 milligrams
  • Folate: 1,000 micrograms
  • Vitamin B12: No UL
  • Pantothenic acid: No UL
  • Biotin: No UL

Figuring Out Fatigue

Fatigue can have myriad causes, from poor sleep to the early signs of cancer. If you are taking supplements in conservative doses, but you feel abnormally tired, there could be many other reasons. Although the fatigue may have coincided with starting the vitamin supplement, it could have also coincided with the beginning of a low-grade virus in your body, an increase in stress at work, a change in exercise activity or diet or countless other potential triggers.

You can try discontinuing the supplement to see if your fatigue goes away. If it doesn't, you should make an appointment with your doctor, who will ask questions and perform tests that can help you get to the root of the problem.

If you are taking excessive doses of nutrients without your doctor's approval — stop. Not only may it be making you sick and tired, but it's likely also a big waste of money.

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