Tibial Stress Fractures - Common in Female Military Recruits
"The findings in this study emphasize the importance of vitamin D status in risk of stress fractures in young women who are taking part in physical activity.
According to the present study, 75% of female [military] recruits were at higher than necessary risk of stress fractures of the tibia & fibula due to low serum 25(OH)D [vitamin D blood levels], less than 40 ng/mL.
The higher risk of stress fractures due to low serum 25(OH)D could be addressed in young women by assuring their serum 25(OH)D concentration is maintained at 40 ng/mL or higher. (equivalent to 100 nmol/L).
[Blood levels of vitamin D] among white women in the highest quartile (40.2 to 112.5; with a mean of 50 ng/mL) were associated with half the risk of stress fractures as those in the lowest quartile (6.5 to 26.9; mean 20 ng/mL).
These results suggest that supplementary vitamin D3 intakes of 2,000 to 4,000 IUs/day would promote bone health and reduce risk of stress fractures, and that the benefits of this intake would exceed its risks."
-Burgi, AA et al, "High Serum 25-Hydroxyvitamin D is Associated with Low Incidence of Stress Fractures," Journal of Bone and Mineral Research Jun 22. doi: 10.1002/jbmr.451. [Epub ahead of print]
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Vitamin D and Stress Fractures in Healthy Young Women Naval Recruits
When this "hot-off-the-press" & "not-yet-published-in-print" article landed on my desk Saturday, I was VERY INTERESTED, to say the least!
If a researcher wanted to find out how important Vitamin D was to preventing stress fractures--what better group to study than the U.S. military?
Lots of fractures. Plenty of raw data just waiting to be researched.
Stress Fractures & Vitamin D - Now That's a Problem Worth Looking Into
Stress fractures, associated with cumulative trauma, are common in new women military recruits. And it turns out--they're a big reason that women leave military service. Now, that's a problem that needs solving.
Researchers from San Diego's Naval Health Research Center, the University of California School of Medicine at San Diego, and the Creighton University School of Medicine in Omaha, Nebraska put their collective heads together to design a study to test their hypothesis: Do low levels of vitamin D contribute to the high rate of stress fractures in boot camp.
Here's what the researchers already knew:
- Vitamin D blood levels need to be at 31 ng/mL, at the minimum, to adequately absorb calcium and maintain bone health.
- Vitamin D deficiency is associated with a higher incidence of fractures in older men & women.
- When Vitamin D blood levels are below 30 ng/mL, the risk of stress fractures increases in young men.
Here's what the researchers wanted to find out:
- Are low blood levels of Vitamin D associated with the risk of stress fractures in young women?
- Does the risk of stress fractures decrease as the Vitamin D blood levels increase--is there a "dose-response" relationship?
Here's how they set out to answer their questions--armed with a database of military & medical records--and a freezer filled with blood samples from new recruits.
- The researchers were able to measure the vitamin D levels of every recruit in this study from the date they first enlisted--which gave them a unique opportunity to see what the women's Vitamin D levels were before any fractures occurred. Turns out, by law, all new recruits have blood samples taken, and these are frozen & made available for research purposes. Very convenient.
- The researchers were able to select 600 women who actually suffered stress fractures of the tibia (shin bone) or fibula (calf bone) during eight-weeks of boot camp & then compared their vitamin D blood levels to a matched-control group of 600 women spared from stress fractures--but who shared the same age, race/ethnicity, and length of service.
- They factored in the season in which each fracture occurred. It might matter.
- The researchers also looked at BMIs (body mass index), and what state each recruit came from. Do they matter?
- This kind of study design would be very difficult to recreate in a non-military environment--which is why the results have important implications for all women.
What We Learned About Vitamin D's Impact on Stress Fractures in the Women's Naval Study
The most important findings:
1. White women in the highest quartile of Vitamin D blood levels (40.2-112.5, with a mean of 50 ng/mL) had half the risk of stress fractures as those in the lowest quartile (6.5-26.9, with a mean of 20 ng/mL). Spun another way, there was double the risk of stress fractures of the tibia & fibula in women with Vitamin D levels of less than 20 ng/mL, compared to those with levels of 40 ng/mL.
2. As Vitamin D levels in white women decreased, their risk of stress fractures increased. It was an inverse dose-response relationship for the risk of stress fractures. Less D--more stress fractures. (note: for a variety of reasons--including skin pigmentation, bone mineral density, & too small of a number of black women with high vitamin D levels--the authors were unable to draw statistically significant associations between Vitamin D levels & stress fractures in black recruits)
3. 75% of women Naval recruits were at a higher than necessary risk of stress fractures of the tibia & fibula due to low Vitamin D levels (<40 ng/mL)
4. A Vitamin D blood level of 40 ng/mL would be the best target for the prevention of stress fractures, the study suggests. This is double what the Institute of Medicine recommended in 1997 as an adequate Vitamin D blood level to maintain bone health. The IOM recommended >20 ng/mL, in spite of previous research that's pinned the minimum level to maintain bone health at >30 ng/mL
5. Latitude didn't make a bit of difference to the recruits' Vitamin D levels. In this study, Vitamin D levels were in no way associated with the recruits' state of residence. On average, the Southerners had the lowest levels of Vitamin D. Maybe they wore more sunscreen? Or drank less milk?
6. BMI was not associated with the risk of stress fractures in this study group.
Recommendations for Vitamin D Supplementation for Active Young Women
The authors make "no bones" about their recommendations for Vitamin D supplementation based on what they learned from the Women's Naval Study.
- They recommend a target of 40 ng/mL for women to prevent stress fractures.
- They suggest that in normal adults, 4000 IUs/day of vitamin D3 would be needed to achieve this target.
- The 2010 Institute of Medicine Report endorsed 4000 IU/day as being the Tolerable Upper Level of Intake (TULI)
- Prevent fractures before boot camp begins. Recruits with low levels of Vitamin D should be identified prior to boot camp--because it may take 2-3 months of supplementation to increase one's blood concentration of Vitamin D to an optimal level for preventing stress fractures.
- Athletic young women are most at risk for stress fractures--they would benefit to achieve the optimal target of 40 ng/mL of Vitamin D.
The article's conclusions:
"Since the risk of fractures increases in older adults, and fractures can occur at any age, Vitamin D supplementaton is recommended for all ages.
However, based on the findings of this study, only serum(OH)D concentrations in highest quintile (39.9 to 112.5 ng/mL) were associated with lower risk of stress fractures. A similar association was present when the comparison was limited to whites. (40.2 to 112/5 ng/mL)
While no randomized trials of Vitamin D3 intakes of 2000-4000 IU/day have been reported, the 2010 Institute of Medicine Report endorsed 4000 IU/day as being the Tolerable Upper Level of Intake (TULI).
(*Full body sun exposure provides the equivalent of 10,000 IU/day, suggesting this may be a physiologic limit. And, Vitamin D supplement intake has been reported to be safe for adults in does up to 9,000 IU/day)
The findings in this study emphasize the importance of Vitamin D status in risk of stress fractures in young women who are taking part in physical activity.
Although this study was conducted in a military population exposed to rigorous physical training over an eight-week period, Vitamin D is also likely to benefit young women in the general population who engage in strenuous physical activity.
This could include females who take part in high school or college athletic programs, marathons and/or triathlons, and moderate to high impact weight-bearing activities.
Recent studies have shown that vitamin D deficiency is highly prevalent in otherwise healthy young people."
Have You Checked Your Vitamin D Level, Lately? How'd You Do?
Do you know what your blood level of Vitamin D is?
You'd be wise to find it out. It's easy to do with a "serum 25(OH)D test".
How else are you going to know if you were deficient? How else are you going to know what Vitamin D dosage you should be taking--or how much time you need to sit in the sun?
Check out Dr. James Dowd's handy dandy chart in one of my earlier posts to give you some idea of how much Vitamin D you would need to take if wanted to get your level up to 40 ng/mL or more. Click here.
If you rely solely on the Institute of Medicine's recommendations, (600 IUs for men & women below age 70) your level may not budge out of the basement. Their guidelines don't take into account all the variables that inhibit absorption of Vitamin D. Sun exposure, season of the year, age, body weight (the heavier you are, the harder it is to absorb vitamin D), or prescription drugs & disease conditions that interfere with absorption. Get a good review on all the variables that affect Vitamin D absorption, here.
If you don't know your Vitamin D blood level, you're "dancing in the dark", when it comes to supplementing.
Does This Study Change Anything for Me?
If preventing hip & spinal fractures as we age is the "name of the bone health game"--then does a study about the effects of Vitamin D on preventing stress fractures in young women have any relevance to older women? I'm betting it does.
I already take 4000 IU/day of Vitamin D3. I'm inside a lot, I'm rarely out in the sun without sunscreen, and I live in a part of the country where there's not enough sunshine to make Vitamin D on my skin for at least 6 months of the year.
In the past, when I supplemented with what seemed like a generous 1800 IUs of Vitamin D, I just barely got over the 31 ng/mL level. Truth be told--I wasn't exactly perfect about taking Vitamin D daily. Rainbow Light Gummies have changed all that.
My physician agrees that 4000 IUs/a day is fine for me. She recommended I take Rainbow Light Sour Lemon Vitamin D Gummies--and since starting them, I rarely miss a day. They taste great--like gummy bears. To read more about that decision, click here.
Do I believe that all I need for healthy bones is to get enough Vitamin D? Of course not! It's far more complicated than that. It's a combination of getting plenty of absorbable calcium--mostly from "real foods", about 15 other minerals, getting enough weight-bearing exercise, maintaining muscle mass, and working on balance. Click here to read more.
My N=1 Study on Vitamin D & Bone Fractures--OK, I admit this probably has no relevance, but......
My oldest son fractured his collarbone (clavicle) when he was 17 months old. He fell off a park bench. It was early Spring---perhaps not much time to make up for the winter's loss of Vitamin D.
Back in 1981, no one was talking about the importance of vitamin D. Who knew from D? And no one had a clue back then that breast-fed babies were at risk for being vitamin D deficient--especially if their mom's were Vitamin D deficient. This kid was breast-fed.
My concern back then was whether or not he was getting enough calcium. The doctor assured me that wasn't a problem.
When this athletic kid went on to fracture his collarbone two more times (different places) while playing sports, first at age 8 (in the winter), & again at age 11, I figured something was going on with this kid's bones. I asked the doctor, a pediatric orthopedist, if my son needed more calcium. What was going on with his bones?
"Not to worry. I've got boys myself. Active kids break bones. My kids have broken bones, and the collarbone is the most common break of all. It happens. Don't worry, he's getting enough calcium. He's not unusual."
Could it have been his lack of Vitamin D? We'll never know. But according to Dr. Michael Holick, one of the foremost authorities on vitamin D, infants who are deficient in vitamin D never attain genetically preprogrammed bone density.
My son's all grown-up, with a son of his own. You better believe this Grandma recommended Vitamin D supplements for her gorgeous grandson--especially while he was breast-feeding. I wasn't taking any chances.
Waiting for the Results of the Vital Trial to Decide on How Much Vitamin D to Take?
If you read the February 1, 2010 New York Times article, "The Miracle of Vitamin D: Sound Science, or Hype" you might be tempted to dismiss the recent research on Vitamin D. I wouldn't advise it. If you want to wait to get your "sunlight fix" or down your Vitamin D supplements until the upcoming Gold Standard randomized control Vital Study is complete--go for it.
I say, "No thanks!" They're still recruiting for this massive randomized-controlled trial of Vitamin D & Vitamin E--and then it will be another 5 years until it's completed. Why wait?
I wouldn't count on its results being conclusive. The study group is too old--with women over 65 & men over 60. The dose is the same for everyone (2000 IUs) which makes no sense when it comes to vitamin D--because base levels of vitamin D vary widely--and vitamin D doses are weight dependent. Heavy people need more than slim people.
Not everyone absorbs Vitamin D equally. Prescriptions interfere with absorption--as do age, and certain disease conditions.
Plus, much of the benefits of taking vitamin D may occur years before a disease may surface--and disease is the endpoint of the Vital Trial--Can Vitamin D supplements affect the incidence of cancer, stroke, or heart disease.
Do you take a Vitamin D supplement that's over the IOM recommendation of 600 IU/day?
Has anyone managed to boost their Vitamin D levels to 40 ng/mL or more?