How long does it take for vitamin supplements to work? It depends on how nutrient deficient you are....

Here's How Long It Actually Takes For A Supplement To Kick In

You probably won’t notice an immediate change.

by Sheila Amir and Molly Burford
Originally Published: 

How long does it take for a supplement to start working? It’s no surprise that this question is one of the top searches on health websites and online forums. You purchased a supplement in hopes of feeling better, and once you’ve started it, you would like to know exactly when this "feeling better" business is going to begin.

However, like most things related to your health, this seemingly simple question has a fairly complex answer. First and foremost, let's define a supplement “working” as the point when you are truly feeling better, and the signs and symptoms you were feeling prior to supplementation begin to notably dissipate. Let's also focus on supplements with research and quality control inspections to vouch for them (aka not encapsulated nonsense).

Choosing A Trustworthy Supplement

In an ideal world, here’s how this situation might play out: Let’s say you were tired, cold, and cranky all the time, and your doctor diagnosed you as having iron deficiency anemia. You took a doctor-recommended iron supplement in addition to following a nutritionist's dietary recommendations. Two to four weeks later, you noticed a bit more pep in your step, so it seemed like your treatment plan was beginning to work. This example is laden with some pretty simple guidance for handling a vitamin deficiency:

  • Noticing your signs and symptoms, rather than ignoring your health and well-being
  • Researching those symptoms and discussing with your healthcare provider, rather than going down the online rabbit hole of self-diagnosis
  • Taking tests to confirm findings, and receiving a supplement recommendation from your doctor
  • Following that up by taking the supplements and eating well, making you an exemplary health student and all-around awesome human being (go you!)

But let’s be real — it doesn’t always happen quite so smoothly. Most of the time, we read an article or blog that mentions symptoms we're managing daily, and then we decide to take whatever supplement mentioned. That can be fine — in fact, if it's a credible source, this is actually how many people start their journey toward health. But if the source is the supplement company itself, or you're reading the article in a moment of hypochondria, then there's a chance that product doesn’t live up to the hype. Read the fine print and do your research before adding supplements (or anything else) to your health routine.

How Long Before The Supplement Starts Working?


Once you’ve found a supplement you feel confident in, here's how to figure out how long it will take for that supplement to start working.

Factor 1: Level of Nutrient Deficiency

One of the biggest factors that dictates how long it takes before a supplement kicks in is how nutrient deficient you are to begin with.

“If a person is more deficient with a particular [nutrient], they will need to take more of that supplement to replenish themselves back to a normal level,” explains Dr. Gregory Glowacki, PharmD. Let's say nutrient stores are like pools. If your pool is empty, it's going to take longer to fill than if your pool is, say, half or mostly full.

Factor 2: Supplement Dosage

The next factor is how much of the supplement you are taking. Going back to that hypothetical pool, it's half full, but if you're only putting in a five-gallon bucket of water each day, it's going to take a very long time to fill it. “For example … how deficient someone is in vitamin D will determine how much vitamin D they [need to] take,” says Dr. Glowacki. “There are many different strengths of vitamin D available over the counter (OTC). If someone has a very high level of vitamin D deficiency, they may need to take a prescription dose, which is much higher than what would be available OTC.”

But you don’t want to overdo it. Put it this way: If you break some laws to steal a fire hose and hook that bad boy up to the hydrant out front of your house, you're probably going to cause some damage to yourself, the pool, a few lawn gnomes, the siding along the house, and everything else. “It is possible to overdose on pretty much anything,” explains Dr. Glowacki. “Vitamins are a good example of this. One way to classify vitamins is on whether or not they are considered to be water soluble or fat soluble.”

What’s the difference between a water soluble vitamin and a fat soluble vitamin? The difference is in how the body gets rid of excess levels of that type of vitamin. With water soluble vitamins, the body will dispel excess levels of vitamins when you pee. However, when it comes to excess levels of fat soluble vitamins, these guys are stored in the fatty tissue of the body and aren’t so easy to remove. “These stores of excess vitamins can lead to toxicity with extremely high doses,” says Dr. Glowacki. “Too much zinc can cause nausea and GI distress; too much calcium can cause constipation (even if it comes from something like Tums); too much magnesium can cause diarrhea.”

Taking mega-doses of supplements is never a good idea. You can reach toxic levels of even water-soluble supplements, and anyone trying to tell you otherwise could probably benefit from a course or two in molecular biology. “Although most of the doses provided OTC are generally safe for most people, it is always a good idea to talk to your doctor or pharmacist before starting a new supplement,” Dr. Glowacki states. Get an expert’s opinion before adding any type of vitamin or supplement to your routine.

Factor 3: Supplement Absorption Rate

Dosage and absorption rate are basically sibling factors. The body can only absorb so many nutrients at a time, just like you can only drink a certain amount of water at a time. Drinking eight to 10 cups of water throughout the day is totally doable and makes you feel awesome. Drinking eight to 10 cups of water all at once is probably not going to end well. The same goes for supplements and spacing out the dosage over time.

There are many different components that can affect the absorption rate of a vitamin or supplement. “The acidity of the stomach, how much food one has consumed, whether or not the supplement is considered to be enteric coated or delayed release, what other medications patients are taking along with the supplement, and even genetics and age are a few things to consider,” says Dr. Glowacki in regards to understanding a vitamin’s efficacy.

Take, for example, the use of slow release iron supplements for iron deficiency. Iron is a metal, and asking your body to absorb metal — especially a lot at once — is a big request. Sure, we need it to survive, but it's still a metal. Throwing a bunch in at once is going to make you feel sick because your cells are all like, “Dude! We only have so many receptor sites! We cannot work under these conditions.” This is why taking mega-doses is a waste of time and money. It's also potentially very dangerous to you.

Factor 4: Supplement Quality

In the U.S., there is no federal regulation on supplements, meaning purchases of vitamins, minerals, and herbs are unregulated by the government. “Supplements are not directly regulated by the FDA,” says Dr. Glowacki. “For this reason, it would be best to look for supplements that have been approved by an organization that has set specific testing standards for quality and purity.” If you're trying to fill the pool with a hose that doesn't function, it's not going to fill.

The Federal Trade Commission (FTC) will come in and retroactively put the smackdown on supplement manufacturers that make fraudulent claims, cause people bodily harm, or are found to have major discrepancies between label and actual contents. However, that means something bad has to happen first. Supplementation inspection of quality is optional and at the company's expense (reputable companies should be totally willing to pay that). It’s up to you to do the research before you buy.

“A good example of this would be United States Pharmacopeia (USP) approved supplements,” Dr. Glowacki says. “When you see a supplement marked with USP, you know that the supplement has been tested and has met the standards set by that organization.”

Factor 5: Other Supplements You’re Taking

All nutrients need other nutrients for their absorption and utilization. If you're supplementing with calcium, magnesium, or zinc, yet deficient in vitamin D, you're not absorbing those minerals as well as you could be.

If you're supplementing with iron, but have a deficiency in vitamin A (beta-carotene), several B vitamins, vitamin C or zinc, you're having issues ranging from absorption to utilization. Ask your doctor which supplements to combine to make sure you’re optimizing your absorption rate.

Factor 6: Cause Of Nutrient Deficiency

What's causing the deficiency in the first place? How did your metaphorical pool become empty? Is it a genetic situation? Is it a side effect of one of your medications? Do you need to make dietary changes? Have you been stressed AF and unaware that stress essentially drains your body of many nutrients, especially zinc?

“Many factors play a role in your absorption of supplements, including other medications you are taking, your level of deficiency, what dose you are taking, and other conditions you may have,” says Dr. Elizabeth Schlosser, PharmD. “Additionally, your own physiology can affect how well supplements are absorbed. This includes other conditions such as celiac disease, inflammatory bowel diseases, or others.”

If you don't resolve what's draining the pool, you may never top it off with water, let alone keep it topped off in the long term. “It is very important to know the cause of your deficiency,” states Dr. Schlosser. “If an underlying condition is causing the deficiency, you may not be able to correct it sufficiently with supplements.”

Factor 7: Your Diet

Remember that the word “supplement” means “in addition to,” not “in place of.” The nutrients we need for health are the same ones we are intended to get from our food.

Speak with a nutrition professional to get legit advice on how to pair your supplemental efforts with a sustainable eating plan. While you get the hang of a new way of eating, taking supplements in addition to your daily meals will help fill in the gaps.

The Takeaway

Quality supplements only work when you take them. How soon they work depends on many factors, and there is no magical moment when you can expect them to kick in. (If only!) So, eat your fruits and vegetables, get some sleep, and keep talking to your doctor. With time, you’ll figure out a plan that works for you.


Dr. Gregory Glowacki, PharmD

Dr. Elizabeth Schlosser, PharmD, BCPS, BCACP, Assistant professor of Population Health at the James L. Winkle College of Pharmacy at the University of Cincinnati

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