Niacin (vitamin B3: here) is generic name for the compounds nicotinic acid and niacinamide. Although classed as a vitamin, niacin can actually be synthesised in the liver from the essential amino acid tryptophan and so it technically only conditionally essential. At lower intakes niacin is essential for the formation of the coenzymes NADH and NADPH and is therefore plays a pivotal role in energy metabolism and synthetic reactions, respectively. However, nicotinic acid also possesses pharmacological activity, the most interesting and well reported of these being the ability of high doses to favourably affect plasma lipoprotein ratios. In this respect, niacin can raise levels of high density lipoprotein (HDL), lower levels of low density lipoprotein (LDL) and lower levels of triglycerides (very low density lipoprotein). Dyslipidaemia is likely a result of the development of a diet induced metabolic disorder, and such a condition increases the risk of cardiovascular disease considerably. Niacin may be a useful treatment for such dyslipidaemia.
Niacin is known to cause cellular changes in insulin sensitive tissues such as liver, heart and skeletal muscle, and this explains its known blood sugar lowering effects at high doses. In particular, niacin treatment at pharmacological doses causes an upregulation of a number of genes including those for PPARδ and PPARγ coactivator-1α in skeletal muscle. Animal studies suggest that the transcription factors PPAR and PPARγ coactivator-1α are important regulators of fatty acid uptake, mitochondrial fatty acid oxidation and oxidative phosphorylation. In addition they may regulate muscle fibre type. For example, endurance exercise increases the expression of skeletal muscle PPAR and PPARγ coactivator-1α, and causes a conversion of type II glycolytic fast twitch fibres to type 1 oxidative slow twitch fibre. This therefore explains the increase uptake and oxidation of fatty acids in endurance trained muscle. In addition, niacin is also able to increase angiogenesis in skeletal muscle, as is endurance exercise, and this increase the capacity of muscle to oxidise fats.
Research has investigated the effects of niacin supplementation in rats at high doses to assess if the changes are similar to those of endurance exercise. Zucker rats (a rat bred for obese characteristics) were fed either a control diet or a diet containing high amounts of niacin at a dose of 750 mg per kg of body weight per day1. Another group of lean rats were also fed a control diet. After 4 weeks on the various diets the rats were analysed and those fed the high niacin diet had a higher percentage of oxidative type I skeletal muscle fibres and higher mRNA levels of genes encoding for muscle fibre type regulation, angiogenesis factors and fatty acid utilisation and oxidative phosphorylation. There was also a higher activity of the mitochondrial enzyme succinate dehydrogenase in those rats fed the high niacin diet. These results suggest that niacin supplementation increased the oxidative capacity of skeletal muscle in rats, in a similar manner to that of endurance exercise, an effect that is likely to be mediated by a number of PPAR genes that are known regulators of muscle fibre type and fatty acid utilisation in skeletal muscle.
Dr Robert Barrington’s Nutritional Recommendation: Pharmacological doses of niacin (the nicotinic acid form of the vitamin; niacinamide does not possess these effect) that cause beneficial effects on blood sugar and lipoprotein levels may have potential health consequences on liver function and should not be attempted without professional guidance. Of course, as the effects of niacin are similar to those experienced by endurance exercise, such physical activity is a potentially better way of experiencing such health changes. However, endurance exercise should be limited as it is a form of stress and too much can be just as damaging as too little.
RdB
