Exercise, Vitamin D, and Trust in Health Hacks

I want to thank the makers of chlorophyll water, detox foot pads, and other contemporary forms of snake oil.

These products don't do what manufacturers claim they do, but at least they help keep us skeptical about new health hacks.

Ideally, we stay skeptical but receptive. There's no evidence that foot pads absorb toxins, but if studies suggest otherwise, we might want to start using them.

(In the meantime, Wormwood Ginger Foot Patch hasn't been found to burn fat or detoxify, and even if it did make your body "a beautiful S curve", would you really want that? It sounds like scoliosis.)

I invite you to stay skeptical as you read this newsletter, because I'll be describing a new study that suggests a simple hack for boosting vitamin D levels.

This struck me as one of the most methodologically rigorous studies I've seen all year, so your skepticism is needed in case I become a bit too enthusiastic.

Why is this important?

So much about Vitamin D is uncertain or debated that for the past 8 years there's been an international conference called "Controversies in Vitamin D".

Al the same, experts do agree on some things. Here are five points of consensus:

1. Vitamin D is an essential nutrient.

We can't survive without this vitamin, but our bodies don't produce it on their own.

2. Vitamin D is essential to bone health.

Vitamin D is needed for mineralization, which increases bone density and strength, as well as remodeling (the removal of old bone tissue as new tissue forms).

3. Vitamin D is critical for physiological processes such as calcium metabolism, muscular and neural function, etc.

A study published yesterday suggests that vitamin D and omega-3 supplements even help preserve telomeres – i.e., protective caps that prevent the ends of chromosomes from degrading or fusing.

Talk about health hacks. If these findings can be trusted, vitamin D/omega-3 supplements might slow aging and the onset of age-related chronic diseases.

(I'll discuss this study in a future newsletter. Age-defying elixirs are among the oldest and mostly widely prevalent forms of snake oil. I remain skeptical but receptive to the notion that a few supplements might slow down the clock – if only a little.)

4. Many people don't have sufficient vitamin D levels.

One widely-cited study found insufficient serum vitamin D levels among 42% of American adults. The percentages were higher among Black and Hispanic people, as well as children.

At the same time, vitamin D levels tend to dip during the winter months, when sunlight is limited. A large 2021 study found that in the UK, 71% of adults show insufficient levels between October and March.

(What would "insufficient" levels be? Following the NIH and others, ideal ranges are routinely described as 20-50 ng/ML, or 50-125 nmol/L, although both lower and higher minimums have been proposed.)

5. The main sources of vitamin D are diet and UV light.

One reason many of us are low in vitamin D is that most foods, by themselves, provide little or none of this nutrient.

Fatty fish are a notable exception. 3 ounces of wild-caught salmon, for instance, provides as much as 81% of the daily value (DV) for an average adult.

Meanwhile, 3 ounces of anything else would not exceed 10% of the DV unless it were fortified (or, in the case of mushrooms, irradiated by UV light).

Most of our dietary vitamin D comes from fortified foods, though a single serving of any one of them probably won't contain much.

For example, a cup of milk provides about 10-19% of the DV, depending on brand. As for dairy products like yogurt and cheese, non-dairy milks, and other foods, some brands are fortified, some aren't. If you care, you have to read the labels.

Supplements are the other main dietary source of vitamin D. A tablespoon of cod liver oil exceeds the DV for vitamin D (and vitamin A, as well as as providing substantial amounts of omega-3 fatty acids).

Other supplements vary widely in vitamin D content. Caution is needed, because some of them exceed the recommended daily maximum of 100 mcg, or 4,000 IU.

(More broadly, supplements should be approached cautiously owing to limits on how they're regulated. They may contain less vitamin D or whatever than claimed, while also containing undisclosed ingredients or contaminants. Third-party certification can provide some reassurance on quality and safety.)

Sunlight is a primary source of vitamin D, because UVB radiation triggers synthesis of vitamin D in the body.

Sunlight and animal foods are sources of vitamin D₃, while plant foods provide D₂. Fortification and supplements may provide either one. These forms of vitamin D are roughly equivalent, though studies suggest that consuming D₃ is slightly more effective at raising blood levels.

How much vitamin D do we need?

Currently, the recommended daily allowance (RDA) for vitamin D is 15 micrograms (600 IU) per day for healthy individuals between 1 and 70. This assumes minimal to zero sunlight.

If you're reading food labels, the FDA's Daily Value (DV) assumes that 20 micrograms (800 IU) per day is suitable for adults eating a 2,000 calorie per day diet, or for children over the age of 4. This too assumes no sunlight.

For those of us who don't live in a cave, it's hard to say how much sunlight we would need for our bodies to produce sufficient vitamin D. This statement from the NIH is both informative and squishy, as befits the current evidence;

"Some expert bodies and vitamin D researchers suggest, for example, that approximately 5–30 minutes of sun exposure, particularly between 10 a.m. and 4 p.m., either daily or at least twice a week to the face, arms, hands, and legs without sunscreen usually leads to sufficient vitamin D synthesis."

Do we need a hack?

Some experts argue that we don't need to worry about vitamin D levels, because humans evolved on a planet where very little of our food provides this nutrient and, in some regions, the sun isn't out much either.

I find a lot wrong with this argument, including the assumption that we can't improve upon the health practices of our prehistoric ancestors.

Owing to modern science (and support from statistics), I think the evidence is clear that many of us don't get enough vitamin D, particularly during the winter months. If our minimum standards are a bit high, fine, many people still have a genuine need.

This brings me to a new study on how we might address the problem.

The new study

This study, led by Oliver Perkin at University of Bath and a team UK researchers, was published in Advanced Science last Monday.

Since vitamin D accumulates in adipose tissue (i.e., body fat), Perkin and colleagues wanted to know whether exercise might cause some of that vitamin D to be released into the bloodstream and benefit us in the usual ways.

This is an intriguing premise for a study. Our bodies already contain the nutrient we're lacking; rather than changing our diets or taking supplements (or spending too much time in the sun), we just need to do something already known to be healthy in order to unlock those hidden stores.

Perkin and colleagues studied a group of sedentary adults who were overweight or obese. (As Dr. Perkin explained in an email to me, there's no reason to doubt that the results would generalize to the rest of the population.)

Participants in the study ranged from ages 25 to 65 but were otherwise comparable in important ways (they didn't smoke, take vitamin D supplements, or report any chronic diseases, for instance).

The fact that participants were comparably sedentary was determined by self-report and by a chest-mounted accelerometer worn for one week before the main part of the study got underway.

You read that right. Participants wore this device for an entire week, just to confirm that they were comparable in activity levels. This gives you a sense of how rigorous the methodology was. I'm leaving a lot out too.

The study took place in the winter (October 1 – April 1), when UVB light in the UK is insufficient for vitamin D synthesis. Participants were divided into two groups:

Exercise group: 21 participants engaged in four cardiovascular exercise sessions per week for 10 weeks. (The total amount of exercise each week was roughly 2 hours and 45 minutes, fairly close to WHO recommendations.)

Control group: 20 participants made no change to their ordinary (i.e., sedentary) lifestyles.

Main findings

Perkin and colleagues examined changes in Vitamin D levels across the 10-week period.

A quick biochemistry note. The substances we call vitamin D undergo a number of transformations in our bodies before they finally benefit us. The active metabolite – the one that strengthens our bones etc. – is called 1,25(OH)₂D₃.

Since this metabolite may not be a reliable indicator of vitamin D levels, the researchers also measured something called 25(OH)D, a precursor to 1,25(OH)₂D₃.

In each case, the main findings were exciting:

• The exercise group showed no changes in 1,25(OH)₂D₃ from the beginning to the end of the 10-week period. The control group dropped by 15%.

• Both groups showed declines in 25(OH)D, but the exercise group dropped 10% less than the control group did.

In short, exercise reduces the usual decline in Vitamin D levels during the winter months. That's the laudably simple takeaway from the study.

Some skepticism

Did the effects of exercise stem from additional sun exposure?

No. Participants exercised indoors – and UVB light was insufficient for the entire 10 weeks of the study anyway.

Did the effects of exercise stem from weight loss?

No. The exercise group didn't lose weight.

Why not? Because the researchers instructed them in advance to increase their food intake, just enough to offset the anticipated effects of exercise.

Aha, I thought when I read that. Here's a fatal flaw. Maybe the exercise group fared better in vitamin D levels because they were eating more than usual, including foods containing vitamin D.

Turns out I was wrong. Via email I described my concern to Oliver Perkin, the lead author. His response:

"It’s a really good question, and something we were cognisant of when designing the study. To avoid this, we elected to guide participants to consume additional quantities of extra foods that were not known to be sources of vitamin D, based on what they reported consuming in their habitual diets via baseline weighed food diaries..."

Indeed, those food diaries revealed no differences between the groups in vitamin D intake.

Finally, personal anecdotes rarely constitute good data, but I can't resist sharing one.

The overdressed person in the photo above is me, in March 2021, suffering through my first winter in the northeast after 31 years in the south. I rarely experienced sunlight that winter and took no supplements, but I did exercise vigorously (I was freezing). I checked this week and my vitamin D levels around that time were higher than they'd been in 2018 and 2019.

Conclusion and practical advice

The new study suggests a simple health hack: By exercising, you can increase your vitamin D levels (or at least prevent them from declining when you're not getting enough sun).

I find this exciting. More research is needed, but I would say, tentatively, that that we can add one more item to the list of benefits that exercise may confer.

Here's some practical advice, based on the assumption that you get an annual physical exam.

1. If your vitamin D levels are in the normal range, and your doctor doesn't recommend additional supplementation for some medical condition, don't adjust your vitamin D intake.

There's no clear evidence that vitamin D supplementation, beyond adequate levels, is a health hack. For instance, extra D won't help ward off COVID-19, as falsely claimed during the pandemic.

2. If your vitamin D levels fall slightly outside the normal range, consider waiting until your next checkup to make adjustments.

Measurements of serum vitamin D levels are fallible. Experts don't fully agree on the boundaries of the normal range anyway. At the same time, nobody seems to believe that a year of slightly low vitamin D levels would be harmful.

3. If your vitamin D levels are low and you attempt to remediate, be careful:

• Spending more time in the sun would help, but overdoing it increases the risk of skin cancer and other problems.

• Eating fatty fish would help, but overdoing it might increase your exposure to mercury and other contaminants.

• Taking vitamin D supplements would help, as long as you don't overdo it.

Finally, my personal favorite:

4. If your vitamin D levels are low, consider exercising more. For most people, exercise offers a variety of benefits, with minimal risks.

Thanks for reading!

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Appendix: The dose-response question

The new study suggests that exercise might benefit vitamin D levels, but it doesn't tell us how much is needed, or whether there's a simple dose-response relationship – i.e., the more you exercise, the higher your serum levels of the vitamin.

I asked Dr. Perkin about this. His view is that the relationship between exercise and vitamin D is too complex and uncertain to be described this way.

For instance, he and his colleagues measured decreases in each participants' adipose and serum vitamin D levels. As he pointed out to me,

"If we had seen a direct relationship between decreases in adipose vitamin D content and serum vitamin D content then that might have suggested there was dose-response relationship, but we did not see that."

In other words, if exercise simply draws the vitamin D out of body fat and adds it to the bloodstream, we might expect that greater amounts of exercise would make more vitamin D available. Evidently the relationship isn't so simple.

Part of the reason may be that some of the vitamin D gets delivered to and released by the muscles. As Dr. Perkin told me,

"We also know that muscle probably takes up, stores, uses, and releases vitamin D too, but we have no idea about the rates of flux, and can only assume that exercise would alter flux rate too."

In short, exercise seems to improve vitamin D levels, but the research is still too new to suggest practical advice on the effects of different types, intensities, or frequencies of exercise.