Vitamin D Status In United States (Is Our Low Status Linked To High Obesity Rates?)

Vitamin D Status In The United States, 2011-2014, American Journal of Clinical Nutrition, May 2019

In conclusion, the prevalence of the US population at risk of vitamin D deficiency has remained fairly stable, ∼5%, over the past decade, from 2003 to 2004 through 2013 to 2014. The prevalence of at risk of vitamin D inadequacy decreased from 21% to 17.7%.

Deficiency was defined as a serum 25 hydroxyvitamin D (25(OH)D) less than 30 nmol/L.
Inadequacy was defined as 30–49 nmol/L.

Housekeeping:
One nmol/L is equal to 0.4 ng/mL
One ng/mL is equal to 2.5 nmol/L
So,
Deficiency: 30 nmol/L = 12 ng/L
Inadequacy: 30–49 nmol/L = 12-20 ng/L

If ~20% of the population is inadequate, that’s not good.

There are 3 ways to increase vitamin D status:
1. Sunshine
2. Supplements
3. Certain conditions lead to lower vitamin D, e.g. obesity, inflammation, some prescription drugs, loss of the part of the bowel where vitamin D is absorbed (upper small intestine).

In that list above, the first two add vitamin D to the system, the last one subtracts it. I don’t think we pay enough attention to that subtraction factor. If we addressed number 3, numbers 1 and 2 would reduce in importance.

Here are three links addressing the problem with obesity (number 3 above):

The link between obesity and low circulating 25-hydroxyvitamin D concentrations: considerations and implications, International Journal of Obesity, March 2012

One potential mechanism by which obesity could contribute to low serum 25-hydroxyvitamin D is adipose sequestration of vitamin D.

The importance of body weight for the dose response relationship of oral vitamin D supplementation and serum 25-hydroxyvitamin D in healthy volunteers, PLoS One, November 2014

BMI, relative to absolute body weight, was found to be the better determinant of 25(OH)D [than dose]. Relative to normal weight subjects, obese and overweight participants had serum 25(OH)D that were on average 19.8 nmol/L and 8.0 nmol/L lower, respectively. … We recommend vitamin D supplementation be 2 to 3 times higher for obese subjects and 1.5 times higher for overweight subjects relative to normal weight subjects.

25-Hydroxyvitamin D response to graded vitamin D₃ supplementation among obese adults, The Journal of Clinical Endocrinology and Metabolism, December 2013

Here, they actually came up with an equation:

The most important outcome of our study is that we were able to quantify the dose needed to raise a person’s 25(OH)D level based on his or her weight:

Additional daily vitamin D3 dose (IU) = [weight (kg) × desired change in 25(OH)D × 2.5] − 10

In other words, we require ∼2.5 IU/kg to raise 25(OH)D by 1 ng/mL. Thus, raising the 25(OH)D level of a 120-kg person by 10 ng/mL would require an average additional daily dose of 2990 IU of vitamin D3.

If that 120 kg (265 lb) person instead weighed 86 kg (190 lb) they would need about 1000 IU less a day (2140 IU instead of 2990 IU). Right? Although, there was a lot of variability in this study: “… given the variability in response, 13 subjects receiving 1000 IU of vitamin D₃ daily achieved a 25(OH)D level >30 ng/mL, whereas 1 subject who received 10,000 IU daily did not reach a 25(OH)D level of 30 ng/mL.”

The CDC says: