Let's look at our D*action data, 7000 members strong... does exercise help vitamin D absorption?

As part of the D*action questionnaire, we ask participants to describe their typical physical activity during the past 12 months. Categories to choose from are: none, mild, moderate or strenuous. Mild physical activity includes activities like gardening, walking or biking for at least 20 minutes, three or more times per week. Activities that usually break a sweat are considered moderate. Activities that always break a sweat are defined as strenuous. We then assign participants to an activity group based on the most vigorous activity they reported.  Participants who engage in less than mild or infrequent activity are grouped together in a 'none/non-regular' activity group.  For outdoor activity, we ask about each season and categorize participants into groups by the activity they engage in for at least half of the year. 

Here are some of our findings:

More than 90% of D*action participants report some level of regular exercise. You are a healthy bunch! Congratulations.

About half of the participants engage in mild or moderate activity and one third engage in strenuous activity.    

What about exercise in relation to vitamin D? We took our data and charted the dose response of each exercise category. The exercisers (mild through strenuous) are the green and blue lines, see how they track almost the same? The red line is the 'none/non-regular' grouping.

This data seems to show that regular exercisers have a slightly higher vitamin D dose response than non-regular exercisers, especially at the lower dosages of vitamin D. What we can't tell from this chart is why. It could be that the exercisers have lower BMIs. It is well known in research that BMI is a factor in vitamin D absorption (the higher the BMI the slower the absorption).

Research on exercise and vitamin D

There is some evidence that exercise may be an independent factor for vitamin D level, but it doesn't seem to be certain. Here are a couple of references.

Sunlight and other Determinants of Circulating 25-Hydroxyvitamin D Levels in Black and White Participants in a Nationwide US Study  

D. Michal Freedman, et al.

National Cancer Institute
Click to View Paper 

Freedman studied around 1500 participants, over 2 years, asking each participant for monthly blood samples and questionnaires. The population was diverse - black and white, male and female, and from different latitudes. The study ran for two years (2008, 2009) and was published in 2011. If you choose to read the paper, please note they report all vitamin D blood samples in nmol/L (divide by 2.5 to get ng/ml).

One of the conclusions from this paper was:

"factors that were most strongly associated with higher circulating 25(OH)D levels in the overall population were increased age, summer and fall blood collection (compared with winter collection), hours outdoors being physically active, and vitamin D supplement intake level. Factors most strongly related to lower 25(OH)D were race (black compared with white) and BMI above 25."

Later in the paper they also state it this way:

" the number of hours being physically active outdoors was a stronger predictor than hours outside also suggests that the character of outside time may be important. Some have suggested that exercise itself, independent of outdoor time, may affect vitamin D levels; however, our finding that indoor physical activity was unrelated to vitamin D levels does not support this hypothesis."

The effects of muscle-building exercise on Vitamin D and mineral metabolism

Dr. Norman H. Bell, et al.

View paper

In this study Bell took fourteen men who had engaged in regular muscle-building exercises for at least 1 year and 14 age-matched controls (age range, 19-36 year). He hospitalized them on a metabolic ward and they were given a constant daily diet that was the same. He then measured many different minerals and vitamins in their blood, including vitamin D.

From the abstract:

"The results indicate that muscle-building exercise is associated with increases in serum Gla-protein, serum 1,25(OH)2D, and urinary cyclic AMP. The increase in serum Gla-protein suggests that this form of exercise enhances bone formation.'

 Vitamin D Success Story

Tell us a little bit about yourself:

My name is Paula Williams.  I am a Registered Dietitian, working in a hospital.  I live in Fort Worth, Texas, am 57 years old, married, and have two children and four grandchildren.

How did you hear about GrassrootsHealth / vitamin D?

I found it online after discovering my own level was low. It was 39 ng/ml even though I did everything I teach!  I consume dairy products, eat fish, take a multivitamin and calcium/D supplement.  I was shocked.  I assumed it would be within the recommended range. My doctor recommended 2000 IU/day.  I did not expect to feel anything.  I felt like a different person after just three weeks of supplements.  

How was your health before vitamin D?

As I became older I noticed I did not have as much energy and started having aches/pains and sensitive teeth. I assumed this was normal aging.

How much vitamin D do you take? How do you get it (sun or supplements)?

I take 2000-4000 IU per day from a combination of supplements and food.  I always wear sunscreen.

What is your vitamin D level?

Last time it was checked it was 92 ng/ml.  I feel 20 years younger. I feel like I'm in my 30's not my 50's. I no longer have the aches/pains and my teeth sensitivity has improved. I rarely catch colds. Looking back, it seemed to come on gradually, so I didn't realize how poorly I was feeling until I started to feel better.  It made me curious about the patients I see. [Note: Grassroots Health recommends vitamin D levels in the range of 40 - 60 ng/ml.]

What would you recommend to others who are in a similar situation?

Everyone should test, otherwise you don't have a baseline and know how much to take.

How do you tell others about vitamin D?

I discuss it with most of the patients I see.  I have worked to get vitamin D level testing in guidelines for certain conditions, such as Sickle Cell Disease & Osteoporosis/falls.

I ask doctors to order the test on those with heart failure, diabetes, MS, heart disease, cancer, lupus and hypertension. I have found patients with levels <4 ng/ml!  

One 35-year old black lady had Transverse Myelitis (which is similar to MS), had a previous stroke, was hypertensive, depressed and bedridden. We checked her level and it was 11 ng/ml. She started supplementing and returned to see me 2 years later. She was then able to walk and her level was up to 70 ng/ml. She said the doctor told her it was a miracle, which may be the case, however I credit the vitamin D. She reported feeling much better and her depression had improved.

I have had mixed response from the doctors.  Many are focused on just treating the illness that led to the admission.  I feel prevention is better than allowing people to develop diabetes, heart disease and cancer.  I feel people deserve to hear about this amazing nutrient.