Two studies published in The New England Journal of Medicine (NEJM) demonstrate that supplementation with n-3 fatty acids and vitamin D did not result in lower incidences of invasive cancer or cardiovascular events when compared with placebos.
Commenting on both papers:
Prof Adrian Martineau, Clinical Professor of Respiratory Infection and Immunity, Queen Mary University of London, said:
“This paper reports eagerly-anticipated findings of a very large trial from the US that was designed to find out whether vitamin D supplementation and/or fish oil can reduce risk of cancer and cardiovascular disease in around 25,000 adults aged 50 years and over. Fish oil was effective in reducing risk of myocardial infractions (heart attacks), but had no beneficial effects on cancer. No benefit of vitamin D in terms of cancer prevention or reduced risk of cardiovascular events was seen in the study population as a whole, although benefits of vitamin D were seen in some sub-groups, with vitamin D supplementation reducing cancer risk in African American participants (who tend to have lower vitamin D status) and those with lower body mass index (who tend to get a bigger boost in vitamin D levels following supplementation than those who are overweight).
“The trial has some notable strengths: it was very large and well-conducted, and the investigators gave a generous dose of vitamin D to participants in the intervention arm (2,000 units per day – 5 times the amount recommended in the UK by Public Health England). However, the study population had pretty good vitamin D status to start with: the average vitamin D level at baseline was 77 nmol/L – much higher than is seen in the UK population, where 1 in 5 people have levels <25 nmol/L. This may reflect the facts that a) dairy products in the US are routinely fortified with vitamin D, and b) 43% of participants were already taking a vitamin D supplement at the start of the trial. So, the relevance of findings relating to vitamin D supplementation from the current study is pretty limited for the UK population – and the jury is still out on the question of whether vitamin D supplements could prevent cancer and/or heart disease in people with low vitamin D levels at baseline. Our own research has shown that other health benefits of vitamin D supplementation, such as prevention of respiratory infections, are strongest in, or restricted to, people who have the lowest vitamin D levels (<25 nmol/L) at baseline. This deficient group was hardly represented in the current study from the USA.
“A similarly large trial needs to be conducted in the UK to find out whether vitamin D supplementation can reduce risk of cancer and heart disease in populations with lower baseline vitamin D status. Such a trial should be large enough to detect modest benefits, since even small protective effects would be likely to prove cost-effective, given that vitamin D supplementation is very inexpensive.”
Prof Jane Armitage, Professor of Clinical Trials & Epidemiology, Nuffield Department of Population Health, University of Oxford, said:
“The VITAL study which randomised over 25,000 previously healthy Americans and followed them for over 5 years has shown that neither vitamin D at 2000 IU per day nor 1 gm a day of fish oils protect against heart problems or cancer. For the fish oils, the results are similar to those seen in other recent reported studies.
“In VITAL they did see fewer heart attacks among those taking the fish oils but with no overall effect on all cardiovascular events this needs to be interpreted cautiously.
“For the vitamin D this has been the best test so far of the effect of vitamin D on heart problems and cancer as most other trials have tested much lower doses. These are important findings as observational studies have suggested that people with higher blood levels of vitamin D live longer, but these results show that this is not due to fewer heart attacks strokes or cancers and there is no clear benefit on these outcomes from taking it regularly.”
Commenting on the vitamin D paper:
Prof Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, said:
“The VITAL trials results do not confirm any magical effect of vitamin D supplementation, at least over 5 years on risks for cancer or heart disease or on death risks, whether or not people had low blood vitamin D levels at the start.
“Whilst authors suggest there may be slight benefits on cancer risks in those with lower weight or black ethnicity, these results must be treated with extreme caution.
“This is one of the largest studies to date and its results confirm a growing suspicion that taking vitamin D supplements is unlikely to protect people from the major killers in our society. Rather, the health community needs to refocus and help people better address the usual risk factors for bad outcomes such as poor diet, low activity levels, smoking, higher blood pressure and cholesterol levels.”
Victoria Taylor, Senior Dietitian, British Heart Foundation, said:
“We don’t recommend taking vitamin and mineral supplements to prevent heart and circulatory disease, and this study’s findings support our advice.
“If you eat a healthy, balanced Mediterranean style diet, you should be able to get all the nutrients that you need to protect you from heart and circulatory diseases.
“But don’t bin those vitamin D supplements just yet; public health guidelines in the UK suggest they should be considered by adults and children over the age of one, especially during autumn and winter, to protect bones, teeth and muscles. If you’re at higher risk of deficiency, its advised that you take these supplements all year round.”
Commenting on the omega-3 paper:
Dr Elizabeth Lund, Independent Nutrition Consultant, previously Research Leader at Quadram Institute of Biological Sciences, Norwich, said:
“This well conducted study confirms analysis of previous studies that suggest taking fish oil capsules will do little to cut the risk of heart disease, stroke or cancer especially if you already eat fish twice a week as is currently recommended. It may be that it is still worth it taking them if you don’t like fish but the study can’t prove that as that was not the question the researchers originally set out to answer.
“There is also good evidence that fish oil capsules do help with the symptoms of arthritis.
“It should be remembered that people who eat fish do tend to be healthier and live longer but it could be something else about eating fish or the types of people who like fish and not specifically the n-3 fatty acids.”
Victoria Taylor, Senior Dietitian at the British Heart Foundation, said:
“In the UK we don’t recommend omega-3 supplements for the prevention of heart and circulatory disease, and the findings of this study support this.
“Although supplements have been recommended in the past for people who have had a heart attack, the guidance changed in 2014 and the same recommendation on fish now applies to everyone; aim for one to two portions of fish a week, one of which is oily.
“But while a supplement of omega-3 may not be helpful in preventing heart and circulatory disease, there are still benefits to eating fish. It’s a nutritious source of protein and including fish in your diet can help you to cut down on your red and processed meat intake.”
Vitamin D paper: ‘Vitamin D supplements and prevention of cancer and cardiovascular disease’ by JoAnn E. Manson et al. was published in the New England Journal of Medicine at 20:00 UK time on Saturday 10 November 2018.
Omega-3 paper: ‘Marine n-3 fatty acids and prevention of cardiovascular disease and cancer’ by JoAnn E. Manson et al. was published in the New England Journal of Medicine at 20:00 UK time on Saturday 10 November 2018.
Prof Adrian Martineau: “I am in receipt of funding from the Medical Research Council (UK) and the National Institutes of Health (USA) to conduct clinical trials of vitamin D supplementation which are currently on-going.”
Prof Naveed Sattar: “No COI.”
Dr Elizabeth Lund: “I have no conflict of interest to declare.”
None others received.