The Sun Exposure Dilemma

Yesterday, we asked you about your policy on sun exposure, and got the above-pictured, below-described, set of answers:

• A little over a third of respondents chose “I recognize the risks, but I think the benefits outweigh them”
• A quarter of respondentschose “I am a creature of the shadows and I avoid the sun at all costs‍♀️”
• A little over a fifth of respondents chose “I recognize the benefits, but I think the risks outweigh them”
• A little under a fifth of respondents chose “I’m a sun-lover! Give me that vitamin D and other benefits!”

All in all, this is perhaps the most even spread of answers we’ve had for Friday mythbuster polls—though the sample size was smaller than it often is.

Of those who added comments, common themes were to mention your local climate, and the importance of sunscreen and/or taking vitamin D supplements.

One subscriber mentioned having lupus and living in Florida, which is a particularly unfortunate combination:

Lupus Foundation | Lupus & UV exposure: What you need to know

Another subscriber wrote:

❝Use a very good sunscreen with a high SPF all the time. Reapply after swimming or as needed! I also wear polarized sunglasses anytime I’m outside.❞

…which are important things to note too, and a lot of people forget!

See also: Who Screens The Sunscreens? (on fearing chemical dangers, vs the protection given)

But, onto today’s science for the topic at hand…

We need to get plenty of sun to get plenty of vitamin D: True or False?

True or False, depending on so many factors—to the point that many people get it wildly wrong in either direction.

Whether we are getting enough vitamin D depends on many circumstances, including:

• The climate (and depending on latitude, time of year) where we live
• Our genes, and especially (but not only) our skintone
• The clothes we wear (or don’t)
• Our diet (and not just “how much vitamin D do we consume”)
• Chronic diseases that affect vitamin D metabolism and/or requirements and/or sensitivity to the sun

For a rundown on these factors and more, check out:

Should I be getting my vitamin D levels checked?

Notably, on the topic of whether you should stay in the sun for longer to get more vitamin D…

❝The body can only produce a certain amount of vitamin D at the time, so staying in the sun any longer than needed (which could be just a few minutes, in a sunny climate) is not going to help increase your vitamin D levels, while it will increase your risk of skin cancer.❞

Source: Dr. Elina Hypponen, professor of Nutritional Epidemiology, and director of the Australian Centre for Precision Health at the University of South Australia Cancer Research Institute.

In contrast, she does also note:

❝During winter, catching enough sun can be difficult, especially if you spend your days confined indoors. Typically, the required exposure increases to two to three hours per week in winter. This is because sunlight exposure can only help produce vitamin D if the UVB rays reach us at the correct angle. So in winter we should regularly spend time outside in the middle of the day to get our dose of vitamin D.❞

See also: Vitamin D & Calcium: Too Much Of A Good Thing?

We can skip the sun and get our vitamin D from diet/supplements: True or False?

True! However, vitamin D is not the only health benefit of sun exposure.

Not only is sunlight-induced serotonin production important for many things ranging from mood to circadian rhythm (which in turn affects many other aspects of health), but also…

While too much sun can cause skin cancer, too little sun could cause other kinds of cancer:

Benefits of Sunlight: A Bright Spot for Human Health

Additionally, according to new research, the circadian rhythm benefits we mentioned above may also have an impact on type 2 diabetes:

Can catching some rays help you fight off type 2 diabetes?

Which way to jump?

A lot of it depends on who you are, ranging from the factors we mentioned earlier, to even such things as “having many moles” or “having blonde hair”.

This latter item, blonde hair, is a dual thing: it’s a matter of genetic factors that align with being prone to being more sensitive to the sun, as well as being a lesser physical barrier to the sun’s rays than dark hair (that can block some UV rays).

So for example, if two people have comparably gray hair now, but one of them used to have dark hair and the other blonde, there will still be a difference in how they suffer damage, or don’t—and yes, even if their skin is visually of the same approximate skintone.

You probably already know for yourself whether you are more likely to burn or tan in the sun, and the former group are less resistant to the sun’s damage… But the latter group are more likely to spend longer in the sun, and accumulate more damage that way.

If you’d like a very comprehensive downloadable, here are the guidelines issued by the UK’s National Institute for Health and Care Excellence:

NICE Guidelines | Sunlight exposure: risks and benefits

…and skip to “At risk groups”, if you don’t want to read the whole thing; “Skin type” is also an important subsection.

Writer’s note: genetics are complicated and not everyone will fall neatly into categories, which is why it’s important to know the individual factors.

For example, I am light-skinned with slightly greying dark hair and blue-grey eyes, and/but also have an obscure Sámi gene that means my fair skin makes vitamin D easily, while simultaneously being unusually resistant to burning (I just tan).

And yet! My hobbies include not getting skin cancer, so I tend to still be quite mindful of UV levels in different weathers and times of day, and make choices (schedule, clothing, sunscreen or not) accordingly.

Bottom line:

That big self-perpetuating nuclear explosion in the sky is responsible for many things, good and bad for our health, so be aware of your own risk factors, especially for vitamin D deficiency, and skin cancer.

• If you have a predisposition to both, that’s unfortunate, but diet and supplementation at least can help with the vitamin D while getting modest amounts of sun at most.
• Remember that you can only make so much vitamin D at once, so sunbathing for health benefits need only take a few minutes
• Remember that sunlight is important for our circadian rhythm, which is important for many things.
• That’s governed by specific photoreceptor cells, though, so we don’t need our skin to be exposed for that; we just need to be able to see sunlight.
• If you’re going to be out in the sun, and not covered up, sunscreen is your friend, and yes, that goes for clear cold days under the winter sun too.
• Most phone weather apps these days have a UV index score as part of the data they give. Get used to checking it as often as you’d check for rain.

Stay safe, both ways around!

Is Dairy Scary?

Milk and milk products are popularly enjoyed as a good source of calcium and vitamin D.

In contrast, critics of dairy products (for medical reasons, rather than ethical, which is another matter entirely and beyond the scope of this article) point to risks of cancer, heart disease, and—counterintuitively—osteoporosis. We’ll focus more on the former, but touch on the latter two before closing.

Dairy & Cancer

Evidence is highly conflicting. There are so many studies with so many different results. This is partially explicable by noting that not only is cancer a many-headed beast that comes in more than a hundred different forms and all or any of them may be affected one way or another by a given dietary element, but also… Not all milk is created equal, either!

Joanna Lampe, of the Public Health Sciences division, Fred Hutchinson Cancer Research Center in Seattle, writes:

❝Dairy products are a complex group of foods and composition varies by region, which makes evaluation of their association with disease risk difficult. For most cancers, associations between cancer risk and intake of milk and dairy products have been examined only in a small number of cohort studies, and data are inconsistent or lacking❞

In her systematic review of studies, she noted, for example, that:

• Milk and dairy products contain micronutrients and several bioactive constituents that may influence cancer risk and progression
• There’s probable association between milk intake and lower risk of colorectal cancer
• There’s a probable association between diets high in calcium and increased risk of prostate cancer
• Some studies show an inverse association between intake of cultured dairy products and bladder cancer (i.e., if you eat yogurt you’re less likely to get bladder cancer)

Since that systemic review was undertaken, more research has been conducted, and the results are… Not conclusive, but converging towards a conclusion:

• Dairy products can increase or decrease cancer risk
• The increase in cancer risk seems strongest when milk is consumed in quantities that result in too much calcium. When it comes to calcium, you can absolutely have too much of a good thing—just ask your arteries!
• The decrease in cancer seems to be mostly, if not exclusively, from fermented dairy products. This usually means yogurts. The benefit here is not from the milk itself, but rather from the gut-friendly bacteria.

You may be wondering: “Hardened arteries, gut microbiome health? I thought we were talking about cancer?” and yes we are. No part of your health is an island unrelated to other parts of your health. One thing can lead to another. Sometimes we know how and why, sometimes we don’t, but it’s best to not ignore the data.

The bottom line on dairy products and cancer is:

• Consuming dairy products in general is probably fine
• Yogurt, specifically, is probably beneficial

Dairy and Heart Disease

The reason for the concern is clear enough: it’s largely assumed to be a matter of saturated fat intake.

The best combination of “large” and “recent” that we found was a three-cohort longitudinal study in 2019, which pretty much confirms what was found in smaller or less recent studies:

• There is some evidence to suggest that consumption of dairy can increase all-cause mortality in general, and death from (cancer and) cardiovascular disease in particular
• The evidence is not, however, overwhelming. It is marginal.

Dairy and Osteoporosis

Does dairy cause osteoporosis? Research here tends to fall into one of two categories when it comes to conclusions, so we’ll give an example of each:

1. “Results are conflicting, saying yes/no/maybe, and basically we just don’t know”
2. “Results are conflicting, but look: cross-sectional and case-control studies say yes; cohort studies say maybe or no; we prefer the cohort studies”

See them for yourself:

1. Osteoporosis: Is milk a kindness or a curse?
2. Consumption of milk and dairy products and risk of osteoporosis and hip fracture

Conclusion: really, the jury is very much still out on this one

Summary:

• Moderate consumption of dairy products is almost certainly fine
• More specifically: it probably has some (small) pros and some (small) cons
• Yogurt is almost certainly healthier than other dairy products, and is almost universally considered a healthy food (assuming not being full of added sugar etc, of course)
• If you’re going to have non-dairy alternatives to milk, choose wisely!

That’s all we have time for today, but perhaps in a future edition we’ll do a run-down of the pros and cons of various dairy alternatives!