Kiwi scientists say laser technology could help quality-test fish oil supplements - recently revealed to lack much of the contents their labels claim in many cases.

Fish oil supplements are commonly used in New Zealand and around the world, with their manufacturers promoting benefits to healthy brain, heart and liver function.

But, in recent years, scientists have cast doubt on the quality and claimed benefits of fish oil supplements, which were sensitive to oxidisation - or "going off" - if exposed to air, light or certain temperatures.

One 2015 study by the University of Auckland's Liggins Institute tested 36 different brands of fish oil capsules, finding that just three contained the same concentrations of omega-3 fatty acids as listed on the label.

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Their analysis revealed that the products contained an average of just 68 per cent of the claimed content, more than two thirds of supplements tested contained less than 67 per cent, and two products only included only a third of what was on the label.

In a just-published study, scientists at Plant and Food Research and Otago University suggest Raman spectroscopy could be used for testing omega-3 and other health-enhancing polyunsaturated fatty acids (PUFA) in soft gel capsules, such as those used in fish oil supplements.

The researchers explored the approach as a means for establishing the concentration of PUFA in capsules, testing the consistency of this concentration across individual capsules, and distinguishing oil that may have become oxidised beyond acceptable limits.

Raman spectroscopy involves directing a laser at the target material, in this case the capsule and oil, and measuring the small fraction of light that is scattered.

The scattered light provides a fingerprint of the chemical composition of the oil as well as other useful information.

The researchers used 11 brands of PUFA oil capsules commonly available on New Zealand shelves, which included five fish oil and six omega-3 concentrate brands.

"Our analysis of Raman spectral variance allowed us to generate models for a range of saturated, monounsaturated and polyunsaturated fatty acids," Plant and Food Research marine products scientist Dr Daniel Killeen said.

"Although the sample size was relatively small, the preliminary results strongly suggest that the method is a useful tool for rapid quality control of soft gel capsules without compromising the structure of the capsule itself.

"Interestingly, in performing our research, we found the concentration of omega-3 oils across all 11 commercially available samples to be in-line with their label claims, which should give consumers reassurance regarding the quality of the oil in the capsules."

Raman spectroscopy involves directing a laser at the target material and measuring the small fraction of light that is scattered. Photo / Supplied
Raman spectroscopy involves directing a laser at the target material and measuring the small fraction of light that is scattered. Photo / Supplied

The study also revealed that Raman spectroscopy could be used to distinguish capsules where the oil may have become oxidised to an unacceptable level.

"Polyunsaturated oils are vulnerable to oxidation, especially at higher temperatures and when exposed to UV radiation," Killeen said.

"Some studies have associated oxidised fish oil with negative health outcomes."

The researchers filled empty capsules with oil that had been deliberately oxidised and compared the results with the unoxidised oil in the purchased capsules.

"We found Raman spectroscopy to have high sensitivity for distinguishing fresh oils from those that had been oxidised.

"This positions the method as a faster, more direct and more sensitive way to identify oxidation in fish oils than other approaches," Killeen said.

"The deficiency of polyunsaturated fatty acids, such as omega-3 in the Western diet has created a high global demand for dietary supplements, such as fish oil.

"This makes rapid and effective quality control methods highly desirable to give consumers assurance and help producers in markets with strict regulations."

However, Liggins researcher Professor Wayne Cutfield, who co-led the fish oil studies, questioned whether the technology was actually ready to do what the scientists claimed it could.

"They haven't validated against a quantified method - it's more of a qualitative, descriptive method - so turning it into quantification like they've tried to do isn't quite real," Cutfield said.

"It's interesting technology and clearly it would help the industry, given the issues that have been flagged already by us and others around the world, however it still requires some more validation."

Cutfield said he welcomed any new method that could quality-test supplements.

"I think consumers deserve to know that what they are buying is good to go - and that hasn't been the case."

Monthly vitamin D doses won't lower heart risk: researcher

Meanwhile, a major research trial by the University of Auckland's School of Population Health has found that taking higher doses of vitamin D once a month won't lower your risk of heart disease.

The trial, led by the university's Dr Robert Scragg, a professor of epidemiology, was conducted over three years using roughly 5,100 adults.

Previous studies have reported increased incidence of cardiovascular disease (CVD) among people with low levels of vitamin D.

But earlier, randomised clinical trials of vitamin D supplementation have not found an effect, possibly because of using too low a dose of vitamin D.

The researchers tracked the heart health of roughly 5,100 adults aged between 50 and 84 from April 2011 through to November 2012, with follow-ups until July 2015.

The participants were mostly from family practices in Auckland.

About one-quarter were vitamin D deficient at the start of the trial - registering vitamin D levels of less than 50 nanomoles per litre via blood tests.

Half the group received a high-dose vitamin D supplement once a month, with an initial dose of 200,000 International Units (IUs).

That was followed by a regular monthly dose of 100,000 IUs.

The other half received a monthly regimen of placebo supplements.

The trial continued for more than three years, on average.

But in the end, nearly 12 per cent of both groups had developed some form of heart disease, the researchers found.

And the risk for developing high blood pressure and/or experiencing a heart attack, stroke, heart failure or angina was more or less the same whether or not a participant had begun the study deficient in vitamin D.

"While the findings rule out monthly dosing of the vitamin for preventing cardiovascular disease, the effects of daily or weekly dosing require further study," said Scragg, whose findings have been published in the journal JAMA Cardiology.

"Ongoing research also will determine within the next three to four years whether vitamin D supplements prevent other diseases."

The possibility that UV radiation, through a mechanism that involves vitamin D, may protect against cardiovascular disease was initially proposed in 1981.

Results from recent meta-analyses have confirmed that people with low vitamin D status have increased risk of CVD.

The theory that vitamin D is protective against heart disease has been around since the 1980s.

Natural sources of vitamin D include ultraviolet radiation from the sun and researchers noticed that the rates of cardiovascular disease were much higher in the winter when the body had lower levels of vitamin D.

Vitamin D is also found in foods such as fatty fish, fortified dairy and egg yolks.