Your nutrient needs shift meaningfully as you age, driven by growth, hormonal changes, and how well your body absorbs what you eat. Some vitamins matter from birth onward, while others become critical only at specific life stages. Here’s what the evidence supports for each age group, with the specific amounts that matter.
Infants and Toddlers
Vitamin D is the priority from day one. All babies need 400 IU of vitamin D daily beginning shortly after birth. This is especially important for breastfed infants and those getting a mix of breast milk and formula, since breast milk alone doesn’t supply enough. The only exception: babies who drink 32 ounces or more of infant formula per day are already getting adequate vitamin D from the formula itself.
Teens: Calcium and Iron Take Center Stage
Adolescence is when your body builds more bone than at any other point in life. The recommended calcium intake for teens aged 14 to 18 is 1,300 mg per day, paired with 600 to 1,000 IU of vitamin D to help the body actually use that calcium. Most teens fall short on both, particularly those who avoid dairy or spend little time outdoors.
Iron needs also spike during the teen years, but they split along gender lines. Boys need about 11 mg per day to support their growth spurt. Girls need 15 mg per day because menstruation adds a consistent source of iron loss on top of growth demands. Teenage girls are at particularly high risk for iron deficiency, especially if their diets are low in red meat and other sources of easily absorbed iron.
Women of Childbearing Age: Folate Before Pregnancy
The CDC recommends that all women capable of becoming pregnant get 400 micrograms of folic acid every day, even if pregnancy isn’t planned. The reason is timing: neural tube defects in a developing baby occur very early, often before a woman knows she’s pregnant. Having adequate folate already circulating in your body is what provides protection. A standard daily multivitamin typically contains this amount. Iron remains important as well for women who menstruate.
Adult Men: Zinc and Magnesium
For men between 20 and 50, the nutrients most often under-discussed are zinc and magnesium. The recommended daily intake for zinc is 11 mg for adult men, and it plays roles in immune function, wound healing, and cell division. Most men eating a varied diet with meat, shellfish, or legumes will meet this target, but vegetarians and vegans often fall short since plant-based zinc is harder for the body to absorb.
Magnesium supports hundreds of enzyme reactions in the body, including muscle and nerve function, blood sugar regulation, and sleep quality. Many men don’t reach the recommended 400 to 420 mg per day through diet alone, particularly if their meals lean heavily on processed foods. Dark leafy greens, nuts, seeds, and whole grains are the richest food sources.
Adults Over 50: B12 Absorption Drops
Vitamin B12 becomes a genuine concern after 50 because your body gets progressively worse at extracting it from food. The reason is physical: as you age, your stomach produces less acid and less of the protein (called intrinsic factor) needed to pull B12 out of meat, fish, and dairy. The lining of your intestines also changes, with shorter, less efficient structures for absorbing nutrients. By 70, this decline is significant enough that deficiency becomes common even among people eating plenty of animal products.
Common heartburn medications (proton pump inhibitors and H2 blockers) make the problem worse by further reducing stomach acid. If you’ve been on one of these long-term, your B12 levels deserve attention. The RDA for adults is 2.4 micrograms per day, but the synthetic form found in supplements and fortified foods doesn’t require stomach acid to absorb, which is why supplementation or fortified cereals are often more reliable than food alone for this age group.
Menopause and Beyond: Bones Need More Than Calcium
After menopause, the drop in estrogen accelerates bone loss. Calcium and vitamin D are the well-known response, but vitamin K2 plays an underappreciated role. K2 helps direct calcium into your bones and away from your arteries. Without enough K2, you can end up with a “calcium paradox,” where your skeleton doesn’t get enough calcium while your blood vessels accumulate too much.
Research on post-menopausal women has found that K2 supplementation can slow age-related bone density loss. One three-year trial showed that a relatively low daily dose of 180 micrograms of a specific form of K2 (called MK-7) slowed bone density decline while improving vitamin K status. K2 is found naturally in fermented foods like natto, certain cheeses, and egg yolks, but supplementation is common since dietary intake tends to be low in Western diets.
Seniors 70 and Older: Higher Targets for Vitamin D and Calcium
After 70, the recommended calcium intake rises to 1,200 mg per day for both men and women. This reflects the accelerating rate of bone loss and the increased fracture risk that comes with it. Vitamin D recommendations also increase, with many guidelines suggesting 800 to 1,000 IU daily for this age group, since aging skin produces less vitamin D from sunlight and kidneys become less efficient at converting it to its active form.
B12 supplementation remains important or becomes even more so. The combination of reduced stomach acid, medications, and decreased appetite means seniors are the age group most likely to be deficient in B12, which can cause fatigue, memory problems, and nerve damage that mimics other age-related conditions.
How to Know If You’re Actually Deficient
A blood test is the only reliable way to know your vitamin D status. The NIH defines the levels this way: below 12 ng/mL is outright deficiency, 12 to 20 ng/mL is inadequate for bone and overall health, and 20 ng/mL or above is generally considered sufficient. Levels above 50 ng/mL can cause harm, so more is not always better. Your doctor can order this test as part of routine bloodwork, and it’s especially worth requesting if you’re over 50, have dark skin, live at a northern latitude, or spend most of your time indoors.
B12 and iron levels can also be checked with simple blood tests. Symptoms of B12 deficiency (tingling in hands or feet, fatigue, difficulty concentrating) overlap with so many other conditions that blood work is the only way to confirm it.
The Risks of Taking Too Much
Fat-soluble vitamins (A, D, E, and K) accumulate in your body rather than being flushed out in urine, which makes overdose possible if you’re taking high-dose supplements without monitoring.
- Vitamin A toxicity causes headaches, nausea, blurred vision, liver damage, and increased fracture risk. It can also cause birth defects, making excessive intake especially dangerous during pregnancy.
- Vitamin D has an upper limit of 4,000 IU per day for adults. That’s only two to four times the amount in many high-dose supplements, so it’s easier to exceed than people realize.
- Vitamin E in supplement form has been linked to increased bleeding risk, including hemorrhagic stroke. One large trial found that men taking 400 IU daily had a higher rate of prostate cancer. Getting vitamin E from food carries no such risk.
- Vitamin K has no official upper limit, but very high doses can damage red blood cells and the liver.
The pattern is consistent: nutrients from food are almost always safe, while supplements create real risk when taken in doses above what your body needs. A standard multivitamin matching RDA levels is unlikely to cause harm, but stacking multiple supplements, especially fat-soluble ones, without knowing your baseline levels is where people get into trouble.