News
Insufficient vitamin D supply in winter
14 January 2010
Current intake recommendations for vitamin D need to be increased by five, says a new study.
01 December 2015
In 2000, the USA Institute of Medicine (IoM) noted that the amount of vitamin E necessary to maintain the correct metabolism of polyunsaturated fatty acids (PUFAs) in cell membranes is related to the intake of PUFAs. A recent review by Raederstorff et al. examines in detail the relationship between PUFA intake and vitamin E requirement. The basal metabolic requirement of 3 to 4 mg/day α-tocopherol needs to be increased to 12.5 to 20 mg/day, just to balance out typical intakes of PUFAs in the Western diet.
The key function of vitamin E in cell membranes is as an antioxidant. Whilst all isoforms of vitamin E have some antioxidant ability, it is the RRR α-tocopherol that has the highest in vivo bioactivity. It is also the only isoform to be bound by a specific transfer protein (α-TTP) which protects the molecule within the cell and prevents it from undergoing the fate of rapid degradation that befalls all the other isoforms. The antioxidant ability of vitamin E is due to the 6-hydroxy group on the chromanol ring which is the active site for scavenging free radicals. The tocopherol radical, once formed, is stable and unable to react further – which breaks the chain of oxidation events (otherwise the reaction would continue to propagate). This essential role of vitamin E has been recognized by the European Food Safety Authority (EFSA) who, after reviewing all available evidence, concluded that “vitamin E contributes to the protection of cell constituents from oxidative damage” (3).
Early animal studies in the 1960s revealed that the relative quantities of α-tocopherol necessary to protect one mole of LCPUFA with 1:2:3:4:5:6 double bonds were 0.3:2:3:4:5:6 respectively (2). The Elgin study conducted between 1953 and 1967 conducted human trials with vitamin E:PUFA ratios. They determined that humans have a basal metabolic requirement of 3 to 4 mg/day α-tocopherol if PUFAs are absent from their diet. A long term diet of 60 g/day corn oil required an increase of α-tocopherol to 30 mg/day to prevent a decrease in the erythrocyte hemolysis test values.
The incorporation of α-tocopherol into the cell membrane leads to a decrease in cell fluidity. α-tocopherol seems to accumulate in the unstructured areas (i.e., not the lipid rafts) which often have high concentrations of the highly unstable PUFA docosahexaenoic acid (DHA). High concentrations of α-tocopherol are also found on the cell membrane surface. Here, if it is in the α-tocopheroxy radical form, it is able to be regenerated by ascorbic acid at the hydrophilic/hydrophobic interface.
Taking into account current average PUFA intakes in the Westernized diet (specifically oleic acid, the omega-6 fatty acids: linoleic acid and arachidonic acid and the omega-3 fatty acids: α-linolenic acid, DHA and EPA), Raederstorff et al. (2) calculated a total daily requirement of α-tocopherol of between 12.5 and 20 mg vitamin E to account for the PUFA intake.
14 January 2010
Current intake recommendations for vitamin D need to be increased by five, says a new study.
1 March 2012
The use of medication worldwide is growing continually, not least because of the rising age of the population. Today there are many people who take more than three different kinds of medication daily (1,2). In highly developed countries, it is particularly common for patients to be prescribed medication long-term, most frequently for the treatment of widespread chronic diseases, such as hypertension, diabetes and hypercholesterolemia. It is also a common practice in those regions to take over-the-counter medicines, including painkillers and medication for stomach ulcers (3,4). When several kinds of medication are taken concomitantly, the risks and side effects increase. In contrast to other adverse drug reactions, the inter-action between medications and micronutrients is only gradually gaining the attention of experts and the wider public. A number of medicines influence the metabolism of vitamins, minerals and trace elements in such a way that they could lead to insufficiencies or even deficiency symptoms in patients (5,6).
23 February 2016
Systolic hypertension is a major risk factor for the onset of strokes and cardiovascular disease. A new double-blinded, randomized controlled trial (1) has shown that a daily dose of fish oil containing 0.7 mg docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) taken for eight weeks was able to reduce systolic blood pressure by a clinically significant 5 mmHg in adults with systolic hypertension.