Should patients be reaching for supplements to stave off these all-too-common illnesses? Rod Tucker investigates

The NHS recommends that we should all be taking a vitamin D supplement during the autumn and winter months for bone and muscle health, although as I mentioned in a previous blog, the value of this advice is debateable.

In recent years, several lines of evidence point to a potentially preventative role for vitamin D in cancer. Indeed, one of the hallmarks of cancer is inflammation and there is some evidence that patients with low levels of vitamin D have higher levels of inflammatory markers in their blood. In fact, low levels of vitamin D have been found to be associated with increased mortality, respiratory and cardiovascular events.

Some evidence even suggests that vitamin D deficiency is harmful to those with coronary heart disease because it increases the level of inflammatory markers. As observational studies have linked low levels of vitamin D to increased mortality this has led to increased use of supplement use amongst those with chronic health conditions.

These studies point to potentially compelling evidence that vitamin D has a far wider range of health benefits than simply strengthening our bones. Moreover, given that in the UK it has been estimated that one in five people are vitamin D deficient, ensuring adequate levels may have important public health implications.

Examining the evidence

But before we raise vitamin D to the status of a health panacea, how robust is the evidence? Since cancer and cardiovascular disease lead to the untimely death of a large number of people, especially as we age, studying the impact of vitamin D in older patients would be able to shed more light on its value.

This is exactly what was done in a recent study published in the journal Clinical Chemistry. The paper discusses the results obtained from a subset of 1561 individuals from a much larger randomised, double-blind, placebo-controlled study in which patients were given either vitamin D and omega-3 fish oils, vitamin D alone, omega-3 fish oils alone or placebo.

The study was designed to test the impact of these supplements on the incidence of cancer and cardiovascular disease. It enrolled over 25,000 people aged 50 and above and followed them for a median of 5.3 years. They measured the inflammatory markers interleukin-6, tumour necrosis factor and C-reactive protein all of which are common biomarkers for systemic inflammation.

The clinical chemistry paper reported that after 12 months of supplementation, there was no reduction in the level of any of the biomarkers among patients although among those given vitamin D alone, there was an 8% increase in interleukin-6 which the researchers were unable to explain. In the larger study, vitamin D alone had no impact on the incidence of cancer or major cardiovascular events (eg stroke, heart attack or death from heart disease) compared to placebo. Equally, there was no impact on cancer or cardiovascular events in those taking the omega-3 fish oils.

What to tell patients

But was this a fluke finding and how do the results compare with other studies? High dose supplementation with vitamin D was shown to have no impact on cardiovascular disease in older adults followed for three years or on the incidence of cancer. Similarly, use of omega-3 fish oils in patients with diabetes but without evidence of cardiovascular disease followed for seven years, did not have a positive impact on vascular events such as heart attack nor did supplementation prevent the development of diabetes in another study.

Dissemination of the results from observational studies are widely reported in the media and this had led to growth in the dietary supplements market. In particular, older adults take supplements to maintain their health as they age.  

Nevertheless, observational studies can only hint at whether a particular supplement is having an effect and cannot show that the supplement and health outcome are causally related. This can only be determined from a randomised trial.

Patients need access to the facts to enable them to make an informed decision and pharmacists can help them make such decisions. Though commonly taken by patients, at the present time, the available evidence suggests that there are limited benefits to be gained from supplementing with either vitamin D or omega-3 fish oils.

Until further studies can refute these data, patients should be advised against taking such products in the hope of achieving better health because they are probably just wasting their money.