Most people use supplements because their diet alone doesn’t provide enough of certain nutrients. That’s not a personal failing. National survey data from NHANES show that 94.3% of the U.S. population falls short of the daily requirement for vitamin D from food alone, 52.2% for magnesium, and 44.1% for calcium. Even with good intentions at the grocery store, closing those gaps through meals can be surprisingly difficult.
But filling nutritional gaps is only one reason. Supplements serve different purposes at different life stages, support athletic performance, and in some cases help reduce the risk of serious health conditions. Here’s a closer look at the evidence behind each use.
Most Diets Leave Nutritional Gaps
The simplest reason to use supplements is that almost no one eats a perfect diet. A large national survey of over 16,000 Americans found widespread shortfalls in several vitamins and minerals when looking at food intake alone. Beyond vitamin D and magnesium, 88.5% of people fell short on vitamin E, 43% on vitamin A, and nearly 39% on vitamin C. These aren’t exotic nutrients. They’re found in everyday fruits, vegetables, nuts, and dairy, yet most people still don’t get enough.
Part of the problem is that the food itself has changed. Research tracking the nutrient content of fruits and vegetables over the past 50 to 70 years shows significant declines across the board. Calcium levels in common produce have dropped 16 to 46%, iron has fallen 24 to 32%, and zinc has decreased 27 to 59%. Some individual foods show even steeper losses: broccoli lost more than half its calcium, collard greens lost 81% of their iron, and watercress lost 88% of its iron content between 1975 and 1997. High-yielding crop varieties, changes in soil quality, and modern farming practices all play a role. The spinach on your plate today is measurably less nutritious than the spinach your grandparents ate.
A daily multivitamin or targeted single-nutrient supplement can help bridge these gaps, particularly for vitamin D in northern climates, magnesium for people who don’t eat many leafy greens or nuts, and iron for people with higher needs.
Certain Life Stages Create Higher Demands
Your body’s nutritional needs shift dramatically depending on your age, sex, and whether you’re pregnant. Some of these increased demands are nearly impossible to meet through food alone.
The clearest example is folic acid during pregnancy. Taking 400 micrograms daily before conception and through the first trimester prevents more than 50% of neural tube defects like spina bifida. For women who’ve had a previous pregnancy affected by a neural tube defect, a higher dose reduced recurrence by 71% in a landmark clinical trial. The American Academy of Pediatrics and the U.S. Public Health Service recommend that all women of childbearing age take folic acid daily, not just those actively trying to conceive, because many pregnancies are unplanned and the critical window for brain and spinal cord development occurs in the earliest weeks.
Older adults face their own challenges. The body’s ability to absorb vitamin B12 from food declines with age, making supplementation common after 50. Calcium and vitamin D become more important for bone health as you age, especially for postmenopausal women. And people who follow vegetarian or vegan diets may need to supplement B12, iron, and omega-3 fatty acids that are difficult to obtain from plant sources alone.
Athletic Performance and Recovery
For people who exercise regularly, certain supplements have strong evidence behind them. Creatine is the most studied. When combined with resistance training, people taking creatine gained roughly double the muscle thickness compared to those training without it. In one meta-analysis, upper arm muscles grew 16 to 20% in the creatine group versus 2 to 6% in the placebo group. Lower body muscles showed similar patterns, with knee extensors gaining about 11% with creatine compared to about 6% without.
These aren’t marginal differences. For someone investing time in strength training, creatine represents one of the few legal, well-researched supplements that reliably accelerates results. It works by helping your muscles regenerate energy faster during short, intense efforts, which lets you train harder and recover more quickly between sets.
Reducing Cardiovascular Risk
Omega-3 fatty acids, the type found in fish oil, have been studied extensively for heart health. A major analysis found that omega-3 supplementation reduced the risk of heart attack by 13%. The VITAL trial, one of the largest studies on healthy adults, found a 28% reduction in heart attack risk as a secondary outcome. These are meaningful numbers for something available over the counter, though the benefits appear strongest in people who don’t already eat fatty fish regularly.
The effects aren’t dramatic enough to replace other heart-protective habits like exercise, maintaining a healthy weight, and not smoking. But for people with low fish intake or elevated cardiovascular risk, omega-3 supplements add a layer of protection backed by large-scale clinical evidence.
Not All Supplements Are Created Equal
Unlike prescription drugs, supplements don’t require FDA approval before they reach store shelves. Under the 1994 Dietary Supplement Health and Education Act, manufacturers are responsible for ensuring their products are safe, but the FDA can only step in after a product is already on the market and shown to be harmful. The burden of proof falls on the government, not the company. This means quality varies enormously from brand to brand.
Third-party certification programs help fill this gap. Look for seals from USP, NSF, or ConsumerLab on the label. These organizations independently test supplements to verify that the product actually contains what the label claims, in the right amounts, free of harmful contaminants, and able to dissolve properly in your body. Products without these seals aren’t necessarily bad, but you’re relying entirely on the manufacturer’s honesty.
Supplements Can Interact With Medications
One reason supplements deserve the same respect as medication is that they can interact with drugs you’re already taking. The interactions with warfarin, a common blood thinner, illustrate the point well. At least nine herbs and supplements have been identified as having major interactions with warfarin, including St. John’s wort, garlic, ginkgo, cranberry, and grapefruit seed extract.
St. John’s wort can reduce warfarin’s effectiveness, leaving you less protected against blood clots. Garlic, on the other hand, can amplify warfarin’s effect. One patient on a stable dose saw their blood-clotting markers more than double after eight weeks of daily garlic supplements, resulting in blood in the urine. In an extreme case, a patient died after drinking cranberry juice daily for six weeks while taking warfarin.
These aren’t obscure interactions with exotic herbs. Garlic, cranberry, and grapefruit are things people consume casually. If you take any prescription medication, checking for supplement interactions is a basic safety step, not optional caution.
Getting the Most From Supplements
How you take a supplement matters almost as much as which one you choose. Fat-soluble vitamins (A, D, E, and K) need dietary fat to be absorbed properly. Taking a vitamin D capsule on an empty stomach means your body may absorb only a fraction of what’s in the pill. Pairing it with a meal that includes some fat, even a handful of nuts or avocado on toast, makes a real difference.
Timing matters for other supplements too. Iron absorbs better on an empty stomach and when paired with vitamin C, but competes with calcium for absorption. Taking a calcium supplement and an iron supplement at the same meal can reduce how much of each you actually absorb. Spacing them apart by a few hours solves the problem.
Supplements work best when they’re targeted to a real need rather than taken as a blanket insurance policy. A blood test can reveal whether you’re low in vitamin D, B12, or iron, turning supplementation from guesswork into precision. The goal isn’t to replace a healthy diet but to cover the gaps that even a good diet leaves behind.