How long does it take for vitamins to work?

You may think you’re deficient in an essential nutrient, you may know your diet isn’t always as good as it could be, or a healthcare provider suggested you increase your intake of a specific vitamin for a health condition. Whatever the reason, if you take any vitamin supplements on a regular basis, you’re not alone: more than half of all Americans 20 and older report taking one or more vitamins to boost their health in some way.

The vitamin industry is booming, but there’s a lot of confusion about whether or not we’re taking the right vitamins in the right ways (and if the way we’re taking our vitamins allows us actually to reap all their potential benefits). Part of the confusion comes from the wide variety of ways in which vitamins “work” or are used and absorbed by the body. For example, if you started taking vitamin D last week, should it be working now? And if it is, how can you tell?

Many factors affect how fast a vitamin begins to work for you, including its formulation, your deficiency level, and how water-soluble it is. Read on to learn more about how your body processes the supplemental vitamins you take, what to expect when you start taking a new vitamin, and how to help your vitamins work better for you.

How long does it take for vitamins to work?

It depends on what type of vitamin you’re taking. There are two main types: fat-soluble and water-soluble. Fat-soluble vitamins are absorbed and stored by fat cells. Water-soluble vitamins are absorbed by the water in your body and then flushed out of your system through your urine rather than stored.

Of the 13 essential vitamins, most are water-soluble; only vitamins A, D, E, and K are fat-soluble. Water-soluble vitamins are absorbed faster, with most being absorbed within a few hours after consumption, according to Kelsey Costa, MS, RDN, dietitian and owner of Nutrition Insights. In contrast, fat-soluble vitamins can take weeks to take effect. However, depending on the amounts consumed, the time to maximum absorption can vary. 

What other factors can change a vitamin’s rate of absorption? How you take it (i.e., swallowing a pill versus drinking a powder stirred into water), any other foods or drinks you consume when you take it, other medications you’re on, and certain GI conditions that affect how your intestines absorb nutrients.

How do you know when vitamins are working?

Some types of vitamin deficiencies don’t cause obvious signs or symptoms, so you may only know you’re lacking one or more important nutrients unless your provider performs a vitamin deficiency test. However, according to Inna Melamed, Pharm.D., functional medicine practitioner and author of Digestive Reset, the most common types of vitamin deficiencies are for nutrients like iron, B6 and B12, magnesium, and vitamin D. 

While the signs of deficiency vary for each of these vitamins, some common symptoms of vitamin deficiency include:         

• Fatigue
• Bone pain
• Muscle weakness
• Shortness of breath
• Dry skin and/or brittle nails
• Hair loss
• Irregular heartbeat
• Trouble sleeping
• Depression

If you’re deficient in a nutrient, it may be easier to tell when your vitamins are working than if you’re taking a vitamin for more general wellness purposes. That’s because it may be easier to notice when some of your deficiency symptoms start to go away. For example, says Dr. Melamed, if you’re low in iron and start taking an iron supplement, you might feel an increase in energy levels; if you’re deficient in magnesium, you may see improvements in sleep habits and bowel movements with supplementation.

These improvements can happen quickly, often in just a few days, but keep in mind that the effects may not be permanent. Dr. Melamed says some conditions, like chronic anemia, are chronic and will need constant replenishment of nutrients.

Costa says it’s not possible to know for certain whether your vitamins are working in other situations (i.e., when you’re not deficient) without a blood test. Instead, you might perceive an increase in energy or a feeling of enhanced well-being, but be mindful that there may be a placebo effect affecting your perception of how much better you feel.

Factors that affect vitamin efficacy

There’s a lot of overlap between the things that make a vitamin more efficacious and the things that affect a vitamin’s absorption rate; after all, if you’re not absorbing much of a vitamin, it’s not going to work very well for you!

The amount of a nutrient your body can absorb and use is called bioavailability. This isn’t the same as how much of the nutrient is included in any particular vitamin you take; a single dose of vitamin C might have 500 milligrams, but that doesn’t mean your body is using 500 milligrams of vitamin C with every tablet.

While some things that influence how much of a nutrient you absorb and use are out of your hands, other things—like when and how you take them and which formulations or types you choose—can help your vitamins work better and faster.

Current vitamin levels

If you have a nutritional deficiency, taking a vitamin is a good way to increase your nutrient levels and see potentially quick, beneficial effects on your health. But suppose you’re not deficient in a nutrient and are supplementing with it anyway. In that case, your body will either not absorb it and flush it out of your system (in the case of water-soluble vitamins) or will hold onto all the excess nutrients, sometimes to your detriment (in the case of fat-soluble vitamins). For example, taking too much vitamin D can lead to toxicity and cause a buildup of calcium in your blood, which may cause vomiting, muscle weakness, and increased thirst. Either way, how much of a nutrient you already have in your body can affect a vitamin’s efficacy.

Formulation  

When thinking about how to make your vitamins work more quickly, it’s important to understand the different meanings of the words “form” or “formulation.” The formulation of a vitamin might mean how it’s sold and ingested, such as tablet, powder, or liquid, or the specific composition of a vitamin and what it’s been mixed with, like magnesium citrate versus magnesium oxide. The types of formulations can make a difference in how well your vitamins work for you. 

Dr. Melamed says that liquid forms of vitamins often have a better absorption rate than pills, especially if you have any digestive issues that might slow down absorption time. Meanwhile, different compound forms of vitamins often have different absorption and efficacy rates. Magnesium citrate, for example, is magnesium combined with citric acid, and it’s generally absorbed well—offering more bioavailability—than magnesium oxide or magnesium combined with oxygen ions.

Age

As you get older, your body becomes less effective at absorbing and using nutrients. A 2022 study reports that calcium, vitamin D, and vitamin B12 are especially difficult for older people to absorb. Additionally, older people are more likely to have health conditions that affect how well nutrients are absorbed, such as liver and kidney diseases. They may also be more likely to be taking medications that can interfere with the absorption of nutrients. For example, many heartburn medications can decrease vitamin absorption.

Timing

Some vitamins are best taken on an empty stomach to avoid potential interactions with foods or other supplements that hinder their absorption, says Costa. For example, calcium and iron should be taken separately from each other since they compete for absorption in the body. 

The time of day you take your vitamins can also affect how well they work. Some vitamins, like magnesium, are known for relaxing muscles and aiding sleep, so it might be smart to take them at night. Vitamin D supplements, on the other hand, are often recommended as a morning vitamin, says Dr. Melamed, who notes that vitamin D is a nutrient that works more like a hormone and is best taken at the start of your day. 

Finally, take note of what type of vitamin you’re consuming and what other dietary choices you’re making: some experts suggest taking water-soluble vitamins on an empty stomach with a large glass of water to help them be better absorbed, and taking fat-soluble vitamins with food, especially, food containing a healthy fat like avocado or fatty fish, to speed absorption.

Medications and health conditions

Many medications and several health conditions can affect how well your body absorbs nutrients. Taking antibiotics long-term, for example, can alter your gut bacteria and decrease the levels of B-complex vitamins in your body, says Costa.

Other medications known to cause nutrient depletion—which can include blocking the absorption of vitamins or increasing how much of the vitamin is flushed out of your system—include:

• Antiepileptic drugs
• Antacids
• Blood thinners
• Proton pump inhibitors
• Diuretics
• Diabetes medications
• Steroids
• Oral contraceptives

Costa says that people with digestive or gastrointestinal disorders and those who have had gastrointestinal surgery may also have difficulty absorbing nutrients. He explains that people with celiac disease or Crohn’s disease may not be able to absorb fat-soluble vitamins as well as other people due to damage or inflammation in the small intestine.

How does your body use vitamins?

Your body needs vitamins to perform a wide range of essential functions, says Costa, from maintaining healthy skin and bones to strengthening the immune system. Whether a vitamin is fat- or water-soluble determines what your body does with that vitamin after you’ve ingested it, as well as where it’s processed and whether or not it’s stored long-term.

According to Costa, water-soluble vitamins are absorbed in the intestines, transported by the cells there, and are not stored, so they need to be consumed on a regular basis; fat-soluble vitamins, however, use the dietary fat in your digestive system to spread out through the body, being stored in the liver, skeletal muscles, and fatty tissues for later use. That doesn’t mean you won’t ever need to replete your levels, but fat-soluble vitamins build up in your system and last much longer than water-soluble vitamins.

The bottom line

Water-soluble vitamins, like vitamin C, B6, and B12, are absorbed quickly and easily but also don’t remain in your system for very long. Fat-soluble vitamins are processed by your body’s fat cells, which means it takes longer for them to work, but they can be stored and used for longer, too. Many things can affect how vitamins are absorbed and, ultimately, how well they work for you, but some of the most common factors include your existing nutrient level, your age, and other medications you take.