Drilling into the data on vitamin D

It’s winter so do we need to take vitamin D supplements? Professor Robert Scragg sheds light on the subject.

Professor Robert Scragg is the Head of the School of Population Health.
Professor Robert Scragg is the Head of the School of Population Health. Photo: Elise Manahan

Professor Robert Scragg describes himself as a bit of a data nerd, but it’s a vital skill to have in the field of health research.

“There are huge opportunities working with big data,” says Robert, Head of the School of Population Health.

“We have a core group of researchers and staff who can analyse data, but we need to grow that, through our training of undergraduates.”

From 2022, a new introductory paper to teach students how to analyse health data, called Quantitative Methods for Health Sciences, will be compulsory for all second-year Health Science students.

Robert, who has been at the University since 1984, has spent a lot of time over his career teaching students to analyse data so they can support the work of researchers. His own research, including cardiovascular disease and cot death, has moved recently into vitamin D.

In simple terms, vitamin D is important for bone and muscle health. It is needed to regulate the body’s calcium and prevent a reduction in bone density. It may have a role in improving non-skeletal diseases and cancer mortality but definitive results are not yet available from clinical trials. While there have been observational studies showing that people with seasonal affective disorder (SAD) have low vitamin D levels, the jury is out until randomised clinical trials are done.

Vitamin D is mainly produced in the skin after exposure to UVB from sunlight, and then processed by the body to become metabolically active.

The most recent Ministry of Health data available, from the Adult Nutrition Survey but now more than a decade old, shows around five percent of people have vitamin D deficiency – that is, less than 25 nanomoles per litre (nmol/L) of blood – and should take supplements. A further 27 percent have levels of 25-50 nmol/L, which is considered vitamin D insufficiency. The prevalence of vitamin D deficiency is higher in Māori (six percent) and Pacific (ten percent). South Asian people aren’t included in that study but it’s known that more than 15 percent are vitamin D-deficient. The figure is higher during winter and spring.

The types of fish that have vitamin D are in the northern Atlantic, such as mackerel, which we don’t eat a lot of.

Professor Robert Scragg University of Auckland

Robert was involved in what’s believed to be New Zealand’s largest clinical trial carried out by one research group, known as the Vitamin D Assessment (ViDA) study, which ended in 2015. In it, international researchers investigated whether high doses of supplementary vitamin D could reduce incidence of heart attacks, fractures and respiratory infections, among other health issues.

There were several significant findings along the way, although many weren’t so clear-cut.

“This was an intervention study, where you actively change something, i.e. give vitamin D to see if there’s a benefit,” says Robert. “We did a large trial with a high dose. We picked a dose we knew would take people up to a vitamin D level that was associated with the lowest risk of disease.”

What the ViDA study showed, as did a similar study in the US called VITAL, was that vitamin D has no effect against the main diseases in people who already had good levels of the vitamin.

“But in the subgroup, who had low vitamin D levels to start with, we see a bona fide range of effects. For instance, in people taking non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, there were beneficial effects for those who initially had low vitamin D and were then supplemented. There was a reduction in the need to take these drugs in those people, but no effect in the total sample.”

The same was true in measures of bone mineral density, lung function and arterial function.

“So if the people in this study had low vitamin D levels, we saw a health benefit for some outcomes after receiving the vitamin D supplements.”

The findings are of potential importance and more research is being done overseas to corroborate the ViDA results.

Photo of sunshine and blue sky
Photo: iStock

The problem is, UVB makes vitamin D and the proportion of UVB in sunlight is maximal when the sun is directly overhead. It’s tricky.

Professor Robert Scragg, Head of School of Population Health University of Auckland

In sunny New Zealand it’s hard to believe people would have low vitamin D levels, but we do. The required level for good health at all ages is deemed to be at least 50 nanomoles per litre (nmol/L) of blood. The ViDA study showed that 20 percent of Pākehā participants, 39 percent of Māori, 47 percent of Pacific and 72 percent of South Asian participants had less than 50 nmol/L.

“Pacific people have higher vitamin D levels than South Asian even though their skin colour is similar, largely because they have a higher meat consumption. South Asian people are primarily vegetarian, but there’s a lot of vitamin D in meat.”

He says it’s a misconception that there’s a lot of vitamin D in eggs.

“Hardly any, and also the types of fish that have it are in the northern Atlantic, fish such as mackerel, which we don’t eat a lot of.”

Robert says there are several ways to deal with that. The first would be to find everyone with low vitamin D levels and supplement them. The second is to try to get the whole population to move in a particular direction and increase their vitamin D levels.

“Some countries have active vitamin D fortification programmes for food, but we don’t. That would be an easy way to reduce the number of people with very low levels.”

There’s also a tricky conflict between avoiding the sun for its skin-cancer dangers and getting enough of it for a vitamin D boost.

“Our studies indicate you can’t get enough sunlight in Christchurch, for example, to boost vitamin D levels, particularly in winter. So, the other population-based strategy is increasing sun exposure, but of course that’s controversial.”

He says sunblock doesn’t stop your body making vitamin D because we don’t apply it evenly or thickly enough. It can get through the gaps on the skin. “The problem is the time of day that we go out. The advice from the Cancer Society and the Ministry of Health is we should only be in the sun at the beginning and end of the day.

“The problem is, UVB makes vitamin D and the proportion of UVB in sunlight is maximal when the sun is directly overhead. It’s tricky.”

People can also buy vitamin D supplements over the counter fairly cheaply, and they don’t need to have a blood test to determine if their vitamin D levels are low first.

“Vitamin D is very safe and you need to take more than 40,000 IU (1,000 mcg) a day for many months before you start getting signs of toxicity. The dose of 3,300 IU a day (about 80 mcg) used in the ViDA study was shown to be safe.

“If a person is only taking 2,000 IU a day, it’s very unlikely to have an adverse effect, although if their vitamin D levels were already good they won’t get any benefit.”

He says people who are indoors a lot, such as those in retirement villages, should take supplements.

“If residents can’t get outside at least weekly, then they would likely benefit from vitamin D supplements, particularly in winter. The evidence is convincing that vitamin D slows bone mineral density loss which is a risk factor for fractures. I would recommend 1,000 to 2,000 IU per day (25 to 50 mcg), particularly in winter when benefit from supplements will be greatest.”

He says if a person is outdoors regularly, there is no need for supplements in summer.

The ViDA study showed that 20 percent of Pākehā participants, 39 percent of Māori, 47 percent of Pacific and 72 percent of South Asians had low vitamin D levels. 

Some people may have been put off vitamin D supplementation because of bad press from one overseas study.

“There was one large US study called the Women’s Health Initiative that followed about 36,000 American women for seven years. They were given vitamin D and calcium together, versus placebo. Some women got kidney stones.

“I believe it was the calcium that did it, but unfortunately vitamin D got bad press because of that. Our ViDA data didn’t find any adverse effects from vitamin D.”

One of the University’s former doctoral students, Arezoo Malihi, now a research fellow, has also analysed adverse events reported in a four-year trial of people taking vitamin D supplements and done a meta-analysis of all clinical trials.

“Her work has shown that vitamin D does not cause kidney stones.”

Robert’s vitamin D expertise sees him called on to peer-review research and he says it can be frustrating when poorly constructed studies are amplified through the media.

“For example, there have been observational studies published that show people with Covid-19 have low vitamin D levels,” says Robert.

“But they don’t go into the factors as to why they have low levels. Having dark skin contributes to lower vitamin D, for example.

“As well, being overweight or poor can contribute to low levels.

“There was a big international trial I was asked to review that had major methodological flaws in it. This is an example of where you can do a study, and call it a trial, but you may have introduced biases into it. Next thing you know, it’s being quoted as gospel.”

Robert was born in Sydney but spent his early years in Papua New Guinea. He did his medical training and PhD in Adelaide and worked in hospitals as a resident medical doctor in Australia for three years before taking the epidemiology path. In July 2019 he took over as head of the School of Population Health after Professor Ngaire Kerse became the Joyce Cook Chair in Ageing Well.

Outside of work, he has a choice of scenic spots to ensure his own dose of vitamin D.

“There are several acres of native bush where I live in the Waitākeres that I like to maintain – exotic weeds are a continuous challenge,” says Robert. “And, when time permits, I’m lucky to have the west coast beaches close by.”

Denise Montgomery

This feature first appeared in the June 2021 edition of UniNews