Two new studies suggest that vitamin D supplements are protective against heart conditions in older people.

An Australian study found that long term use of vitamin D is associated with a small reduction in the risk of major cardiovascular events such as heart attacks among people aged over 60.

A Finnish study found that taking “higher-than-recommended doses of vitamin D for five years reduced the risk of atrial fibrillation in older men and women”.

It’s presumed this would have a knock-on effect of reducing one’s risk for stroke.

The heart and vitamin D, a paradox

On the one hand, observational studies “have consistently shown a link between vitamin D levels and CVD risk”.

Namely, that people who have a vitamin D deficiency – or simply don’t taker a supplement – are seen to develop CVD and subsequent catastrophic events such as heart failure or stroke or death.

In these observational studies, a large group of participants are split between those who regularly take vitamin D supplements and those who don’t.

A number of years go by. Then there’s a follow-up to see who had a heart attack or stroke or developed cardiovascular disease.

The results are nearly always the same: significantly more of those participants who didn’t take a vitamin D supplement developed heart disease.

Often, in these studies, the intake of vitamin D – frequency and dose – are self-reported, which compromises of the reliability of recorded data.

Still, the consistency of the results has prompted one camp of researchers to assume something helpful is going on.

On the other hand

On the other hand, “randomised controlled trials have found no evidence that vitamin D supplements prevent cardiovascular events, possibly due to differences in trial design that can affect results”.

Keep in mind, even if vitamin D fails to prevent a heart attack or stroke, other benefits to the heart have been demonstrated, notably reducing cardiovascular inflammation and atherosclerosis (the clogging of arteries with plaque).

These benefits disappear if you take too much of the supplement. This  supports the idea there is a sweet spot for dosage.

Still, there is a second camp of researchers who have written off Vitamin D as a protective agent for the heart.

Australian researchers tackle this uncertainty

Researchers from the University of Melbourne, University of Sydney, Monash University, the QIMR Berghofer Medical Research Institute (Queensland), and Queensland University of Technology banded together “to address this uncertainty”.

In a big study, called the D-Health Trial, they investigated “whether supplementing older adults with monthly doses of vitamin D alters the rate of major cardiovascular events”.

This undertaken from 2014 to 2020.

It involved 21,315 Australians aged 60-84. The participants randomly received one capsule of either 60,000 IU vitamin D or a placebo.

These were taken orally at the beginning of each month for up to five years.

Some things to keep in mind

Be advised, 60,000 IU is a big dose. Taken daily it would prove toxic, at least for some people.

However, vitamin D is stored in fat tissue. The participants who received the supplement would have basically fed off stored vitamin D over the month.

Also vitamin D aids in the absorption of dietary calcium, which we need for strong bones. People with a vitamin D deficiency absorb no more than 10 per cent to 15 per cent of dietary calcium. In people with sufficient vitamin D levels, calcium absorption increases to 30 per cent to 40 per cent.

Hence, participants in the new study with a history of high calcium levels were excluded.

So were people with an overactive thyroid, kidney stones, soft bones (osteomalacia), sarcoidosis, an inflammatory disease, or those already taking more than 500 IU a day of vitamin D.

Who had a heart attack, who didn’t

During the trial, 1336 participants experienced a major cardiovascular event.

This amounted to 6.6 per cent in the placebo group and 6 per cent in the vitamin D group. A small but not insignificant difference.

The rate of major cardiovascular events was 9 per cent lower in the vitamin D compared with the placebo group. This was equivalent to 5.8 fewer events per 1000 participants.

The rate of heart attack was 19 per cent lower in the vitamin D group. And the rate of coronary revascularisation was 11 per cent lower.

(Coronary revascularisation treatment restores normal blood flow to the heart).

There was no difference in the rate of stroke between the two groups.

Curiously, there was “some indication of a stronger effect in those who were using statins or other cardiovascular drugs.

The researchers suggest this finding warrants further investigation.

Overall, the researchers calculate that 172 people would need to take monthly vitamin D supplements to prevent one major cardiovascular event.

Small difference, but pause for thought

The researchers stress that “the absolute risk difference was small”.

However, they note that theirs “is the largest trial of its kind to date”.

They suggest “further evaluation is warranted, particularly in people taking statins or other cardiovascular disease drugs”.

“In the meantime, these findings suggest that conclusions that vitamin D supplementation does not alter risk of cardiovascular disease are premature,” the authors conclude

To read more about the Finnish study and atrial fibrillation, see here.