Plant-based iron is best absorbed when paired with vitamin C, and vitamin B6 relies on zinc to function optimally, while curcumin the key compound in turmeric is very poorly absorbed unless taken with piperine, which increases absorption by 2, per cent. This pairing system works both ways. For example, zinc and copper compete with one another for absorption in the small intestine. Certain lifestyle factors and habits, such as drinking alcohol and smoking, can cause malabsorption and require a higher intake to maintain an equilibrium.
Caffeine can block the absorption of certain nutrients such as vitamin B6, calcium, iron and magnesium, advises Lenherr. Certain health issues can also impact absorption. This is dependent on each and every person and which vitamin combination they are taking, says Lenherr.
Which is better? Supplements do have a role to play for some groups of people. For instance, people on long-term restrictive weight loss diets or people with malabsorption problems, such as diarrhoea, coeliac disease, cystic fibrosis or pancreatitis, can benefit from supplements. Folic acid supplements are strongly recommended for women planning a pregnancy to reduce the risk having a baby with neural tube defects, like spina bifida.
Also, people who follow vegan diets, especially if pregnant, may benefit from vitamin B12 supplements. If you need to take a supplement, it is best to take multivitamins at the recommended dietary level, rather than single nutrient supplements or high-dose multivitamins.
Many people think that vitamin C helps prevent the common cold. Despite exhaustive research across the world, there is still no strong evidence to prove this. Some studies have shown that taking large doses of vitamin C more than 1, mg per day continuously or when you first develop cold symptoms, may ease some of the symptoms and the duration — on average, making it about half a day shorter.
It does not prevent you catching a cold. You also need to consider the health risks associated with taking large doses of vitamin C. Large doses may cause nausea, abdominal cramps, headaches, fatigue, kidney stones and diarrhoea. Excessive amounts of vitamin C in the body can also interfere with medical tests, such as diabetes tests, giving a false result. Some vitamin and omega-3 fatty acid deficiencies can lead to emotional disturbances.
However, if you are feeling run down, it is more likely to be due to stress, depression or unhealthy lifestyle habits such as insufficient sleep or smoking , rather than a vitamin deficiency. Vitamin E is widely promoted as a beneficial antioxidant that can help prevent heart disease. Unfortunately, several large-scale reviews have conclusively found no evidence that vitamin E supplements prevent death from heart disease. In fact, there may be greater risk of all-cause death from taking such supplements.
Vitamin A in large doses does not cure cancer and can be toxic, particularly if taken as pills rather than food. There is some evidence that vitamin E could play a small role in preventing some cancers although, equally, there is evidence that it could speed up the onset of other types of cancer.
However, this has not been proved or disproved. While it is argued by some that megadoses of antioxidants can help with the effectiveness of conventional cancer treatments, such as chemotherapy and radiotherapy, the evidence is far from supporting this. In fact, it has been shown that megadoses of antioxidants can actually interfere with some medical treatments for cancer by helping to protect the cancer cells that the therapies aim to destroy.
Vitamin E is often singled out as the potential fountain of youth. However, there is no evidence that taking large doses of any vitamin can either stall or reverse the effects of ageing. The table below shows the adequate intake AI for biotin.
Untreated biotin deficiency can cause neurological symptoms, such as seizures, intellectual disability and loss of muscle coordination Deficiency has also been reported in animals fed high amounts of raw egg whites. Egg whites contain a protein called avidin, which prevents the absorption of biotin Biotin does not have any known adverse effects at high doses and the tolerable upper limit has not been established.
Limited evidence suggests that biotin supplements may improve health in those who otherwise get adequate amounts from their diets. For instance, studies suggest biotin may improve symptoms in people with multiple sclerosis MS 47 , Observational studies also indicate that biotin supplements may improve brittle nails in women. However, higher quality studies are needed before any claims can be made 49 , It is found in a wide range of foods. Good sources include organ meats, egg yolk, meat, legumes, cauliflower, mushrooms and nuts.
Deficiency is uncommon and adverse effects are unknown, even at high supplemental doses. Further studies need to establish the tolerable upper intake level. Limited evidence supports the use of biotin supplements among people who already get adequate amounts from their diets.
However, a few studies suggest they may improve the symptoms of MS and strengthen brittle nails. Vitamin B9 was first discovered in yeast, but later isolated from spinach leaves. Vitamin B9 acts as a coenzyme and is essential for cell growth, DNA formation and amino acid metabolism. It is very important during periods of rapid cell division and growth, such as in infancy and pregnancy. Additionally, it is required for the formation of red and white blood cells, so deficiency may lead to anemia.
The chart below presents a few foods that are great sources of vitamin B9 1. Other good sources include leafy greens, legumes, sunflower seeds and asparagus.
Yeast extract spread is exceptionally rich in vitamin B9, providing around 3, mcg per grams. Folic acid is also frequently added to processed food products.
The table below shows the recommended daily allowance RDA for vitamin B9. It also presents the daily tolerable upper limit UL , which is the amount considered safe for most people. Instead, the table shows the adequate intake values.
Vitamin B9 deficiency rarely occurs on its own. It is usually associated with other nutrient deficiencies and a poor diet. Anemia is one of the classic symptoms of vitamin B9 deficiency. It is indistinguishable from the anemia associated with vitamin B12 deficiency Lack of vitamin B9 may also lead to birth defects of the brain or neural chord, collectively known as neural tube defects Yet, studies show that high-dose supplements may mask vitamin B12 deficiency.
Some even suggest that they may worsen the neurological damage associated with vitamin B12 deficiency 53 , Additionally, some scientists are concerned that a high intake of folic acid — a synthetic form of vitamin B9 — may cause health problems. There is not much evidence that folic acid supplements benefit healthy people who are following a balanced diet. A few studies suggest that supplements may reduce the risk of heart disease, improve blood sugar control and slightly reduce the symptoms of depression 55 , 56 , 57 , However, the benefits of taking vitamin B9 supplements may only be seen in those who are low in the vitamin to begin with.
Like all other B vitamins, vitamin B9 acts as a coenzyme. It is essential for cell growth and various key metabolic functions. Deficiency in vitamin B9 is uncommon. The main symptom is anemia, but in pregnant women, low levels also raise the risk of birth defects. For those who get enough vitamin B9 from their diet, the benefits of supplements are unclear.
But studies suggest they may reduce the risk of heart disease and lower blood sugar levels. Vitamin B12 is the only vitamin that contains a metallic element, namely cobalt. For this reason, it is often referred to as cobalamin. There are four main types of vitamin B12 — cyanocobalamin, hydroxocobalamin, adenosylcobalamin and methylcobalamin All of them can be found in supplements, although cyanocobalamin is the most common.
It is considered ideal for supplements due to its stability, but is only found in trace amounts in food. Hydroxocobalamin is the most common naturally occurring form of vitamin B12, and is widely found in animal-sourced foods.
The other natural forms methylcobalamin and adenosylcobalamin have become popular as supplements in recent years. Adequate intake helps maintain brain function and development, neurological function, and the production of red blood cells. It is also required for converting protein and fat into energy and is essential for cell division and DNA synthesis. Animal-sourced foods are virtually the only dietary sources of vitamin B These include meat, dairy products, seafood and eggs.
However, tempeh and a few algae, such as nori seaweed, may also contain small amounts of vitamin B Whether these foods can provide sufficient amounts on their own is a matter of debate 60 , 61 , Other algae, like spirulina, contain pseudovitamin B12, a group of compounds that are similar to vitamin B12, but unusable by the body The table below shows the RDA for vitamin B Those who are at the greatest risk of deficiency are those who never or rarely eat animal-sourced foods.
This includes vegetarians and vegans Deficiency may also develop in older people. In fact, many require regular vitamin B12 injections. Vitamin B12 absorption depends on a protein produced by the stomach called intrinsic factor. As people age, the formation of intrinsic factor may reduce or stop altogether Deficiency may cause various health problems, such as anemia, appetite loss, sore tongue, neurological problems and dementia Only a small proportion of vitamin B12 can be absorbed from the digestive tract.
The amount absorbed depends on the production of intrinsic factor in the stomach. As a result, no adverse effects have been linked with high intake of vitamin B12 in healthy people.
The tolerable upper intake level has not been established. While vitamin B12 supplements benefit people at risk of deficiency, less is known about their effects among those who get adequate amounts from their diets.
One small study suggests that taking 1, mcg per day may improve verbal learning in people recovering from strokes, but more research is needed Additionally, injections of hydroxocobalamin are used to treat cyanide poisoning, usually in combination with sodium thiosulfate Sign in here. We frequently receive questions about how to make sure that a vitamin or other supplement breaks apart properly so that it can be absorbed.
Many people write to tell us that their vitamins won't break apart in tests that they do at home. The question is a good one. To be useful, most supplements must first disintegrate "break apart" and dissolve "go into a liquid solution" in the gut for their ingredients to be absorbed and enter the bloodstream. Pills that don't disintegrate properly can't dissolve and be absorbed; they will simply pass through the body unused. The standard laboratory test for disintegration part of the test known as the United States Pharmacopeia [USP] "Disintegration and Dissolution of Dietary Supplements" method , is an important test of product quality, although passing this test alone does not assure bioavailability — which depends on additional factors such as how well ingredients are absorbed.
During the test, the product under investigation is continuously agitated in warm water for 30 minutes. In that time, the pill should have dissolved or fallen apart to the extent that, if touched, there is no hard core remaining.
This disintegration test is one of the battery of tests to which ConsumerLab.
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