Niacin or nicotinic acid is a B vitamin, designated as vitamin B3, that is vital for our metabolism. It helps us break down foods into energy and build up and repair our body. It can be found in meat and fish products and to a lesser extent in pulses and grains. It is sometimes used by doctors as a treatment for high cholesterol.
What is niacin?
B vitamins all have different structures and vitamin B3 (niacin) is one of the simplest with a ring structure with one arm containing what is called a carboxyl group (COOH). The OH part of the carboxyl group can be swapped easily for an amine group (NH2), and the molecule then becomes nicotinamide. Nicotinamide, like niacin is available in the diet. It is obtained from the breakdown of NAD and NADP (described below) that are found in most plants and animals.
Most of what happens in our body is down to enzymes. These are catalysts, without which our bodies would grind to a halt. Many vitamins are known as coenzymes as they help enzymes do their job. Nicotinamide forms part of two of the most important coenzymes in our body, namely NAD (nicotinamide adenine dinucleotide) and NADP (nicotinamide adenine dinucleotide phosphate). NAD is used by many enzymes that help us get energy from burning our food, while NADP is used by enzymes that help us repair tissues, especially cell membranes.
Additionally NAD is used by enzymes called poly-ribose polymerases (PARPs) to repair DNA, including the telomeres that are thought to set a limit on how old we can be. Too many PARPs however can be damaging1, as they use up a hell of a lot of our NAD.
So to summarize, niacin gives us energy, repairs our membranes and the DNA that helps keep our skin and guts working properly. Lack of niacin in your diet is a serious business, as you'll find out below.
Where can I find niacin?
You will find many cereals are nowadays fortified with niacin, reflecting the fact that most cereals contain niacin in a bound form which is unavailable for use in the human body. However if you are looking for natural sources, then meat and fish provide the most, followed by peanuts, sesame and sunflower seeds and some mushrooms.
Tryptophan is an amino acid that can be used by the human body to produce niacin. It is considered that 1g of tryptophan is capable of providing us with 16mg of niacin. Now, the recommended daily allowance of niacin is set at around 15mg for an average person, indicating that 1g of tryptophan should provide us all we need. However, tryptophan makes up an average of 1% of the protein we eat2. We therefore need to eat 100g of protein or 400kcal of protein to fulfill this need. Strangely enough that is just about achievable for someone eating plenty of meat and fish.
However, during the early 1900s, many poor people in the states of the southern US developed the vitamin B3 deficiency disease, pellagra. Studies carried out at that time showed that having enough tryptrophan was not sufficient to prevent pellagra. Given that their diet contained enough tryptophan, but not enough niacin, these studies make us question the science behind the tryptophan/niacin conversion ratios. It should be noted that the conversion process is known to require adequate vitamin B2, B6 and iron in order to work properly.
In general it is true that B vitamins such as niacin don't work in a vacuum and you really need to ensure that you have enough of all the B vitamins to keep your niacin levels up. As in so many cases a diet of whole foods with minimum junk will help out here. If you are vegetarian then nuts, seeds, mushrooms and seaweed are all good reliable sources.
Over the years some poor cultures have become deficient in vitamin B3. Normally this has been due to a scarcity of meat and fish in the diet, along with the predominance of grains, such as corn or sorghum, that have been processed in modern intensive mills. The over processing of corn and sorghum reduces the niacin content from an already niacin poor grain.
The consequence of serious niacin deficiency is pellagra. Pellagra is known as the disease of the 3 'D's - dermatitis, diarrhoea and dementia. Initially fatigue, indigestion and decreased appetite occur followed by dark skin rashes on parts of the skin exposed to the sun or to heat. The word pellagra coming from the Italian phrase for sour or raw skin (pelle agra). Neurological symptoms such as weakness and tremor can be accompanied by depression and anxiety. Ultimately death occurs, as happened in the southern US in the late 20's when thousands of people died from it.
Interestingly, poor people across the border in Mexico were OK as they traditionally used to soak the corn in slaked lime (calcium hydroxide). Corn does contain niacin, but it is mostly in the form of niacytin, in which niacin is bound to starches or protein fragments (peptides). Treatment with lime releases the niacin from its association with these starches and peptides, freeing it up for absorption in our guts.
Today there are still people suffering with pellagra in various parts of the world. In India and China, where the main dietary staple is the grain, sorghum, it is thought that the amino acid, leucine inhibits any conversion of tryptophan into niacin, thus reducing the potential amount of niacin available from the grain. This is also thought to be a factor with corn based diets also.
Niacin status and disease risk.
Cancer can be caused by damage to our DNA. Niacin has been found to prevent damage to DNA by activating PARP-1s and the P53 tumour suppressor enzyme4. It appears that adequate niacin levels are an important part of our resistance to cancer. Some studies from Italy5,6 have shown a reduced likelihood of certain cancers with increased niacin consumption. Despite this, studies linking niacin levels with cancer incidence are not easy to find, and so it is hard to know exactly how much niacin we should be consuming. It is however very likely to be more than the recommended daily allowance (RDA), which is set at around 15mg per day.
Cardiovascular disease is sometimes treated with high doses of niacin around the 3g per day mark. In particular it is known to reduce LDL cholesterol and triglyceride levels, while raising HDL cholesterol levels. In fact niacin is one of the most potent ways of raising your HDL cholesterol levels. As such some studies have found that large doses over a prolonged period reduce the chance of heart attack and stroke. Interestingly risk of death was not particularly affected. This is perhaps not surprising as low cholesterol levels can damage health as much as high cholesterol levels, but in different ways. There is also a possibility that extremely high doses of niacin (>1g daily) may in themselves be dangerous for certain people (see below).
Individual supplementation of niacin is normally only used to address specific medical conditions, normally under supervision. This is correct in my view, as niacin is a synergistic vitamin that works best with other B vitamins.
As part of a B-complex or multi vitamin levels of niacin vary from 16-100mg. At this level it is unlikely that any harmful side effects will be experienced, although it is possible to experience harmless skin flushing above about 35mg per day. When taking niacin at levels of typically 1.5-3.0 grams per day for prolonged periods it is however common to experience side effects. This is often done under medical supervision to lower cholesterol. This form of supplementation is either done with niacin on its own, or more commonly in combination with another cholesterol lowering drug, such as a statin. Under this scenario the most common side effects are flushing and itching of the skin. Long term supplementation with high doses can lead to serious complications, especially for those with diabetes, peptic ulcers, gout or problems with their liver.
It is possible to get no-flush niacin, but this is not actually niacin, but a closely related substance called inositol hexanicotinate. Its cholesterol lowering effects are not the same as niacin, and so it should probably only be used if you are taking it for other reasons. Thye same applies if you are supplementing nicotinamide.
The niacin content of some example mutlivitamin / B-complex preparations are shown below:
- Nutri - MultiEssentials: 30mg; Multigenics: 70mg; B-Complex: 50mg;
- BioCare - MultiVit and Minerals: 50mg; One-a-Day+: 100mg; B-complex: 50mg;
- Solgar - VM-2000: 100mg; B complex 100: 100mg;
- Healthspan - Multi-vitality Gold: 16mg; B complex 16mg;
For most people it should be possible to get enough niacin from the diet. There are a number of people who would benefit from a supplement that includes niacin along with other B vitamins and synergistic nutrient. For a very few it may be of benefit to use large doses of niacin, but the benefits need to be weighed against the possible side effects.
1) http://europepmc.org/articles/PMC2865187/reload=0;jsessionid=485lOBVBc4V8qpX9y509.6 PARPs - too much of a good thing?
2) http://en.wikipedia.org/wiki/Tryptophan#Dietary_sources Tryptophan only 1% of protein on average.
3) http://www.hindawi.com/journals/jna/2010/157591/ Study of anti-cancer effects of niacin and nicotinamide with good background on the topic.
4) http://www.ncbi.nlm.nih.gov/pubmed/11295153?dopt=Abstract Niacin may reduce cancer risk.
5) http://www.ncbi.nlm.nih.gov/pubmed/10728605?dopt=Abstract Niacin one of a number of nutrients associated with reduced cancer incidence.
6) http://www.ncbi.nlm.nih.gov/pubmed/10797282?dopt=Abstract Niacin one of a number of nutrients associated with reduced cancer incidence.