If you take multiple vitamins and supplements, it can be challenging to know how to time each dosage. Here's the best time to take them and why it matters. 

Why timing matters

You might want to take vitamins and supplements at certain times of the day based on their effects, says Dimitar Marinov, MD, an assistant professor at the Medical University of Varna, Bulgaria.

For example:

• Magnesium helps with relaxation and sleep so it is best taken at dinner, Marinov says.

• Melatonin also induces sleep so you should take it one to two hours before bedtime. 

• Vitamin C can cause indigestion, so some prefer to take it with food to alleviate nausea or constipation. 

Important: While the time of day doesn't change how effectively your body absorbs supplements, whether or not you take them with a meal does. Some vitamins, like B and C, are best to take on an empty stomach while others, like vitamins A and K, need to be taken with foods containing fats for proper absorption.

Best vitamins to take on an empty stomach 

You should take water-soluble vitamins and minerals on an empty stomach as your body will more easily absorb and metabolize them, says Alana Kessler, a registered dietitian and nutrition consultant based in New York City. 

 Water-soluble vitamins dissolve in water and include vitamin C and all B vitamins. You should also take these vitamins with a full glass of water to help break them down for absorption, Stephenson says.

Because these vitamins are most effective when taken on an empty stomach, it is best to take them in the morning, Kessler says. 

B vitamins, in particular, have been shown to boost energy and mood in people who are deficient in them. A 2020 review found that deficiencies in B and C vitamins, iron, and magnesium can cause fatigue, and supplementation can help. 

General advice: Some people are more sensitive to vitamins and find water-soluble vitamins, like vitamin C, upset their stomachs. If this is the case for you, it is ok to take these vitamins with food, Stephenson says. It will reduce their absorption but only by a small amount.

Other vitamins best taken on an empty stomach include:

• Iron. This is because certain foods, especially dairy, can block the absorption of iron. Vitamin C helps your body absorb iron, so if you are taking an iron supplement, it's best to combine that with Vitamin C.

• Probiotics. Some types of probiotics, like ones containing Lactobacillus and Bifidobacterium, have been shown to be most effective when taken up to 30 minutes before a meal.

Best vitamins to take with a meal 

You should take fat-soluble vitamins with meals or snacks that contain fat, such as avocado, egg yolks, or olive oil, for proper absorption. 

Taking these vitamins with food ensures the optimal release of bile and pancreatic enzymes in the stomach that are required for the absorption of fat-soluble vitamins, Marinov says. 

Fat-soluble vitamins include:

• Vitamin D

• Vitamin E

• Vitamin A

• Vitamin K

For some people, it makes the most sense to take these vitamins with a meal, like lunch or dinner, but you don't necessarily have to, Stephenson says. Any food with some fat, like hummus or a handful of nuts, can help break down these vitamins. 

Other supplements that should be taken with food include:

• Calcium carbonate. This is because the stomach acid produced when you eat helps your body absorb this type of calcium. Calcium citrate on the other hand can be taken with or without food, so be sure to check the label to see the kind of calcium your supplement contains. 

• Multivitamins. These contain both water-soluble and fat-soluble vitamins, so take with food to ensure the fat-soluble vitamins are absorbed. 

• Magnesium. Taking magnesium on an empty stomach has a laxative effect and may cause diarrhea. 

When to take prenatal vitamins

Prenatal vitamins typically include both water-soluble and fat-soluble vitamins in one tablet. The best time to take prenatal vitamins could vary depending on your individual health factors, so discuss with your doctor. They also could upset your stomach, so it may help to take them with food.

"Because stomach upset is more likely in pregnancy, I recommend taking prenatal vitamins with food, a small snack with some fat in it is enough," Stephenson says. "This may be the best way to keep the vitamin down, optimally absorb the fat-soluble vitamins, and only minimally impact absorption of the water-soluble vitamins."

Insider's takeaway 

The time of day you take supplements is less important than whether or not you take them with food. Take water-soluble vitamins, like vitamin C and folate on an empty stomach, and fat-soluble vitamins, like vitamins A, E, D, and K with food containing fat to ensure proper absorption. You should also take multivitamins or prenatal vitamins with a snack or meal.

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