The Longevity Nutrients Glossary: Key Micronutrients, What They Do and How Much You Need

Micronutrients are the vitamins and minerals the body needs in small amounts. One influential hypothesis, the triage theory, proposes that modest deficiencies, which it describes as common, speed up molecular aging.⁷ That is a reason to avoid deficiency, not evidence that intakes above the recommended amounts slow aging. This glossary gives the US reference intakes for each nutrient, what it does, who is at risk of low levels and what supplement trials found.

How to read reference intakes

A Recommended Dietary Allowance (RDA) is the daily intake that meets the needs of nearly all healthy people; when the evidence is too thin to set one, an Adequate Intake (AI) is used instead. A Tolerable Upper Intake Level (UL) is the maximum daily intake unlikely to cause adverse health effects.⁸ For vitamin D, the Institute of Medicine concluded that a blood level of at least 20 ng/mL meets the requirements of at least 97.5% of the population, and that higher levels were not consistently associated with greater benefit.¹

The key micronutrients

Vitamin D. Needed for calcium absorption and bone health. The RDA is 600 to 800 IU (15 to 20 µg) a day for adults.² A blood 25-hydroxyvitamin D level of 20 ng/mL or more is enough for most people, the risk of deficiency rises below 12 ng/mL, and levels above 50 ng/mL can be associated with adverse effects.² In the VITAL trial, 2,000 IU a day did not lower the incidence of invasive cancer or cardiovascular events.⁹

Magnesium. A cofactor in energy metabolism and in muscle and nerve function. The RDA is 400 to 420 mg a day for men and 310 to 320 mg for women.⁸ Almost half of Americans got less than the required amount from food in 2005 to 2006.⁵ Magnesium status is hard to assess because most magnesium is inside cells or in bone.^8,10 In a meta-analysis of trials, about 368 mg a day for three months lowered blood pressure by about 2/1.8 mm Hg.¹¹

Zinc. Needed for immune function, wound healing and DNA synthesis. The RDA is 11 mg a day for men and 8 mg for women, and chronic excess can cause copper deficiency.¹²

Vitamin K. Needed for blood clotting and bone proteins. Vitamin K1 comes mainly from green leafy vegetables, and vitamin K2 (menaquinones) from fermented foods such as natto. The Adequate Intake is 120 µg a day for men and 90 µg for women, and vitamin K can interact seriously with warfarin and similar anticoagulants.¹³

Omega-3 fatty acids. EPA and DHA are long-chain omega-3s found in fatty fish; ALA comes from plant oils. The Adequate Intake for ALA is 1.6 g a day for men and 1.1 g for women, and no recommended intake is set for EPA and DHA.¹⁴ The omega-3 index (EPA plus DHA in red blood cells) was proposed as a marker of heart-disease risk, and its developer suggested 8% or more as optimal;¹⁵ the NIH notes that experts have not established normal ranges for blood omega-3 levels.¹⁴ In the VITAL trial, 1 g of fish oil a day did not lower major cardiovascular events or cancer.¹⁶

Vitamin B12. Needed for red blood cells, nerve function and DNA synthesis. The RDA is 2.4 µg a day.⁶ Between 3% and 43% of older adults living in the community, especially those with atrophic gastritis, have low B12, and long-term use of metformin or proton pump inhibitors can lower it.⁶ When a blood B12 result is borderline (150 to 399 pg/mL), a methylmalonic acid test can confirm a deficiency.⁶

Folate (vitamin B9). Needed for DNA synthesis, the methylation cycle and neural tube development. Folic acid and methylfolate both supply it: in a 24-week trial in healthy women they lowered homocysteine equally,¹⁷ and people with two copies of the MTHFR C677T variant responded to folic acid, though they needed more folate than others.¹⁸ Anyone who could become pregnant is advised to take 400 to 800 µg of folic acid daily.¹⁹ Dietary sources include leafy greens, legumes and liver.

Selenium. A constituent of selenoproteins, best known as antioxidants and as catalysts for producing active thyroid hormone, and needed for immune function.²⁰ The RDA is 55 µg a day for adults, and Brazil nuts contain particularly high amounts.²¹ In randomized trials, 200 µg a day did not reduce prostate cancer³ and was linked to a higher risk of type 2 diabetes (hazard ratio 1.55 over an average of 7.7 years).⁴

Iodine. Needed to make thyroid hormone. The RDA is 150 µg a day for adults and the upper limit is 1,100 µg.²² Iodine deficiency is the most common cause of preventable intellectual disability in the world.²² A median urinary iodine of 100 to 199 µg/L shows adequate intake across a population of children and adults; it is a population measure.²²

More is not always better

Upper limits exist because high intakes can cause harm. Long-term vitamin B6 doses of 1 to 6 g a day have caused severe nerve damage, which is part of why the adult upper limit is 100 mg a day.²³ Chronic excess zinc can cause copper deficiency,¹² and 200 µg of selenium a day was linked to more type 2 diabetes.⁴ Before taking a high-dose supplement, check the upper limit on the NIH Office of Dietary Supplements fact sheet for that nutrient.

Should you test?

Routine micronutrient testing is not recommended for everyone. For vitamin D, the US Preventive Services Task Force found the evidence insufficient to judge whether screening adults without symptoms does more good than harm.²⁴ Testing makes most sense when symptoms, diet, medicines or a medical condition point to a specific deficiency, such as low B12 in long-term metformin users.⁶

Derek Giordano

Founder & Editor, IQ Healthspan

Derek Giordano is the founder and editor of IQ Healthspan. A father of four with a lifelong interest in athletics, fitness and the supplement industry, he built the site to show what the research actually supports. Derek is not a physician: articles cite peer-reviewed studies with numbered references you can check, and corrections are logged publicly. Articles are researched, drafted and fact-checked with the help of AI tools, and every claim is checked against the studies it cites. IQ Healthspan has no supplement brand partnerships, affiliate relationships or financial conflicts of interest.

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Sources Listed With Numbered Citations

24 references at the end of this article, checked against PubMed; studies link to their PubMed record