How Long Do Vitamins Stay in Your System? - A Complete Guide

Water-Soluble Vitamins

As the name suggests, the water-soluble vitamins are those that dissolve in water, which means they are more rapidly absorbed into tissues and are metabolized faster than their fat-soluble cousins.

Because they are dissolved in water, any excess of the water-soluble vitamins is excreted through urine and are not stored in the body. As a result, they need to be replenished daily through food or supplementation.

• B1 (thiamine): Functions as a coenzyme in the pentose phosphate pathway, which is a key step involved in the synthesis of fatty acids, steroids, nucleic acids, as well as the aromatic amino acid precursors to several neurotransmitters and other bioactive compounds ¹.
• B2 (riboflavin): Two flavoprotein coenzymes are derived from riboflavin, FMN and FAD, both of which are critical rate-limiting factors in most cellular enzymatic processes, such as the synthesis, conversion, and recycling of niacin, folate, and vitamin B6; synthesis of all heme proteins; co-factors in the metabolism of essential fatty acids; absorption and utilization of iron; and regulating thyroid hormones ¹.
• B3 (niacin): A large number of processes and enzymes involved in several aspects of body function depend on niacin-derived nucleotides like nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP). Aside from supporting energy production, NAD and NADP are also involved in oxidative reactions, antioxidant protection, DNA metabolism and repair, cellular signaling events (via intracellular calcium), and conversion of folate to its tetrahydrofolate derivative ¹.
• B5 (pantothenic acid): Functions as a substrate for the synthesis of coenzyme A (CoA). It plays a significant role in oxidative metabolism, but is also involved in the synthesis of cholesterol, amino acids, phospholipids, and fatty acids ¹. What’s more, B5 is also heavily involved in the synthesis of multiple neurotransmitters and steroid hormones.
• B6 (pyridoxine): Apart from its role in the folate cycle, B6 is required for amino acid metabolism and serves as a rate-limiting cofactor in the synthesis of several neurotransmitters, including dopamine, serotonin, γ-aminobutyric acid (GABA), noradrenaline, and melatonin ¹.
• B7 (biotin): Plays a key role in supporting glucose metabolism and haemostasis, including regulating hepatic glucose uptake, gluconeogenesis (and lipogenesis), insulin receptor transcription, and pancreatic β-cell function ². Deficiency of biotin is rare, but certain pathological conditions can reduce levels.
• B9 (folate) + B12 (cobalamin): Many of the functions of folate and B12 are linked because of their complementary roles in the “folate” and “methionine” cycles. Low levels of B12 can result in a functional folate deficiency, as folate becomes trapped in the form of methyltetrahydrofolate. Proper function of the folate cycle is essential for the synthesis and regeneration of tetrahydrobiopterin, a cofactor for enzymes that convert amino acids to monoamine neurotransmitters (serotonin, melatonin, dopamine, noradrenaline, adrenaline) and nitric oxide ^{3, 4}. They’re also heavily involved in red blood cell production and proper function of the nervous system.
• Vitamin C: The classic role of vitamin C has been tied to immune function by supporting many cellular functions of both the innate and adaptive immune system, as well as supporting epithelial barrier function to protect the body against pathogens. It’s also a powerful antioxidant and serves as a cofactor for several biosynthetic and gene regulatory enzymes ⁵. Research suggests that the vitamin C pool is usually depleted in about 4 to 12 weeks if intake is reduced or stopped, with deficiency symptoms generally starting to manifest after eight weeks ⁶.

With all of that said, the exact time that water-soluble vitamins circulate in your body will depend on factors like age, nutrient status, diet, and the like.

However, most are depleted within 1-2 days, which means replenishing them daily to ensure sufficient levels if critical for optimal health and performance ⁷.

Fat-Soluble Vitamins

Again, as the name suggests, fat-soluble vitamins are a group of four vitamins that dissolve in, you guessed it—fat.

The fat-soluble vitamins are not absorbed directly into the bloodstream, but rather are absorbed into lacteals in the small intestine via chylomicrons and then transported through the lymphatic system before finally being released into the bloodstream ⁸. They are:

• Vitamin A: Its major role is in supporting vision, but recent research suggests it’s also involved in embryonic stem cell differentiation and development, maintaining healthy structure and function of epithelial cells, and regulating macronutrient metabolism of carbohydrates, lipids, and proteins ⁹.
• Vitamin D: A fat-soluble pro-hormone that plays significant roles in maintaining the health of bone, skin, cognition/mood, and the immune response ¹⁰. Low levels of vitamin D have been linked to a number of chronic health conditions.
• Vitamin E: A powerful antioxidant metabolite and an essential dietary factor, vitamin E can be found in two naturally occurring groups: tocopherols and tocotrienols. The properties of vitamin E are largely related to its antioxidant functions, though it also has involvement in a variety of biological activities, including anti-oxidation, anti-proliferation and anti-inflammation ⁹.
• Vitamin K: Vitamin K is heavily involved the blood clotting, as there are several vitamin K-dependent clotting factors, including prothrombin (factor II), factor VII, factor IX, and factor X ¹¹. Insufficient vitamin K can lead to synthesis of nonfunctional clotting factors and cause hemorrhaging.

However, unlike the water-soluble vitamins, an excess of any fat-soluble vitamin doesn’t leave the body through fluids (urine, sweat, etc.), but rather is stored in the liver or adipose tissue for later use ¹².

Studies suggest that although vitamin D is synthesized in the body and excessive intake is rare, vitamin D therapy, even in low quantities of 375 µg/kg for two weeks, can lead to toxicity ¹³. Similarly, vitamin E doses of 400 international units (IU) per day can increase risk of death.

That means that excessive intake of these vitamins can cause toxicity because they are stored anywhere from a few days to several months and levels will accumulate over time. As such, follow directions on supplement labels for safety.