UV-B, Vitamin-D and Covid-19

A star-studded line-up

As the summer days start to draw in, I think it’s safe to send out this post, with apologies any readers in the Northern Hemisphere. Perhaps they should put this one aside for six months.

There’s been recent talk that higher levels of vitamin-D levels are associated with better covid-19 health outcomes. But, while correlation is one thing, causation is another, so any benefits are still controversial. Nevertheless, I’m reminded of the role of personal exposure to UV in the  production of vitamin-D in the skin. Could it therefore play a role in covid-19 survival?

About ten years ago, I was involved with colleagues from Lauder and the Universities of Auckland, Canterbury and Otago in a ground-breaking study that involved hundreds of people wearing personal UV dosimeters for periods of several weeks. Measurements of their vitamin-D* status were taken before and after the exposure periods.

* The pedants out there will tell me off for using such simple language. They’d point out that what’s actually measured is the amount in the blood serum of a substance called “25-hydroxy-vitamin D3” (that mouthful is sometimes abbreviated to 25(OH)D), which is just a marker for vitamin-D status (with concentrations ideally being more than 50 nmol/litre). I’ll bet you’re glad I didn’t bore you with all that.

It’s a few years now since we completed the work, but what we found back then will still apply today, and may be important for our ongoing battle against covid-19.  

First, I was staggered at how little of the available UV Kiwis actually receive. Our study showed that, with our predominantly indoor lifestyles, we’re typically exposed to less than 2 percent of the available ambient UV. And our clothing blocks most of that 2 percent from getting through to our skin. After accounting for clothing coverage, our skin sees less than 0.4 percent of the available dose. I’m a bit annoyed that we didn’t make more of this finding. It’s buried deep an article we published in 2016 (in Table 2 of the paper that’s hidden from the public behind a paywall). Because of those low doses the amount of vitamin-D in our blood typically drops below optimal levels over the winter months.

Second, the current UV doses are so small that most of that decline in vitamin-D status can easily be avoided. All that’s needed a small increase in UV exposure, which can easily be achieved (most of the time) without causing skin damage. The best way is with short sharp exposures to UV with plenty of skin exposed – not just the hands and face.

The UV dose required to stem the decline in vitamin-D status are quite small (less than 0.5 SED of full body exposure per day, compared a dose of 2 or 3 SED for damage to fair skin).

SED is an abbreviation for Standard Erythemal Dose (or a standard dose of sunburning UV). On a summer’s day in New Zealand, the available dose can reach 70 SED, while in winter it can exceed 5 SED even as far south as Invercargill.

The doses needed for vitamin-D sufficiency are quite achievable anywhere in New Zealand during summer with just a minute or two of exposure. Exposures longer than a couple of minutes will be much less effective and could cause skin damage. In fact, sufficient vitamin-D can be made from sunlight in any season except for the depths of winter when to achieve that full-body dose you’d need about 15 minutes of full-body exposure each day in the north (e.g., Kaitaia, latitude 35S), or about 30 minutes of full-body exposure each day in the south (e.g., Dunedin at latitude 45S)  While that may be very interesting to contemplate, it might also be difficult to achieve on a cold winter’s day where I live in Central Otago! Realistically, some clothing will be required, so increasing those exposure times.

With those longer exposure times needed in winter, other sources of vitamin-D may be necessary. There’s little vitamin-D fortification of foods in New Zealand, so in winter - or if you are required to work indoors without the chance for outdoor exposure (the UV needed doesn’t penetrate glass) - it’s worth considering using a vitamin-D supplement. If you can’t get it on prescription, it is readily available over the counter. Others have shown that a dose of 1 or 2 thousand International Units (IU) per day is sufficient to stem the winter decline in vitamin-D status. We already know that such doses are OK because post-menopause women in New Zealand are routinely prescribed 50 thousand IU per month (nearly 2000 IU per day) as part of a standard treatment to prevent bone degeneration (and women live longer than men, so QED 😊).

In Europe, infants are routinely prescribed a daily vitamin-D dose of 400 IU. That’s about the same as in the daily teaspoonful of cod-liver oil that my mum used to give us kids when we were growing up in the 1950s. She was way ahead of her time!

I had to include this example, from the USA - land of whacky units (and even whackier 45th presidents), where 1 “pint” is 475 cc. In the rest of the world it’s 568 ml.

It tasted horrible, so my mum eventually took pity on us and gave it to us in the form of the only slightly more palatable Maltexo ….

Or, better still, in the form of the famous Lanes Emulsion. And what wonderful specimens it produced too! Is that 4 super-healthy generations in one picture?

Of course, you need to be very careful about your UV exposure, especially in summer when there’s enough UV to cause damage to sensitive skins with exposure periods as short as 15 minutes. In fact, there’s so much UV over the course of a summer day, that even using a correctly applied a sunscreen of SPF 30 (which cuts the UV back by a factor of 30) would be insufficient to prevent skin damage - and few sunscreen users apply the product thickly enough to reach the specified performance. Even in the depths of the New Zealand winter there’s enough UV to cause sunburn if you’re outdoors for extended periods.

In a follow-up post I’ll provide details on the amount of UV exposure needed in any situation to optimise your health outcomes for skin damage or vitamin-D. Of course, small doses of UV exposure may produce other health benefits too. For example, they produces endorphins which can amplify feelings of well-being. In any case, I think we can all agree that sitting in the sun is much nicer than just popping a pill.

---

Thanks for listening. Previous posts on the intersection between Ozone, UV, Climate, and Health can be found at my UV & You area at Substack. Click below to subscribe for occasional free updates.