Research Review: Vitamin D and body composition

Research Review:
Vitamin D and body composition

By Helen Kollias

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I’m one of the few people of Mediterranean ancestry that burns in the sun.

I had a pretty good chance at having nice olive skin, since both my parents are bronze, but no — I get the recessive pasty gene. Paternal grandmother pasty + maternal grandfather pasty = pasty grandchild.

Needless to say, between not wanting to turn beet red and listening to all the health recommendations, I put sunscreen on and generally avoid hanging out in the sun at high noon, but have I been harming myself?

Vitamin D: the sunshine vitamin

Vitamin D comes in two versions:

  • D2 from plants
  • D3 from animals

Being animals, let’s look at vitamin D3 or cholecaliferol.

Lucky for us, vitamin D3 is one of the few things that is truly free. All you need is sun and bare skin.

If you hang out in your bathing suit in the sun until you just start to turn pink – not lobster red – your body makes between 10,000 and 50,000 units of vitamin D3! Pretty sweet deal!

A nice sunny day in your Speedo sounds like an overdose, but good news! Your body is smarter than you! If your body makes a ton of vitamin D, it breaks down the extra so you don’t get a D overload.

However, be cautious: Before you go off and chow down on a bunch of vitamin D capsules, you should know that your body can’t regulate orally consumed vitamin D, only vitamin D it makes from the sun.

Once your body makes vitamin D3, though a series of biochemical events, it converts it into 25-hydroxyvitamin D (25-OHD) in your blood. 25-OHD is what your doctor measures to see whether you have enough vitamin D.

For more information about vitamin D, take a look at All About Vitamin D.

Research question

This week, I’ve got two reviews on how vitamin D levels affect body composition, bone, and muscle. Why two? Well, it’s really one study that the researchers split into two articles.

Gilsanz V, Kremer A, Mo AO, Wren TA, Kremer R. Vitamin D status and its relationship to body fat, final height, and peak bone mass in young women. Clin Endocrinol Metab. 2010 Apr;95(4):1595-601. Epub 2010 Feb 17.

Kremer R, Campbell PP, Reinhardt T, Gilsanz V. Vitamin D status and its relationship to body fat, final height, and peak bone mass in young women. J Clin Endocrinol Metab. 2009 Jan;94(1):67-73.

Methods

This study examined young women. On average:

  • they were 19 years old
  • they weighed 68.3 kg (151 lb)
  • they were 162.9 cm (5′ 4”) tall
  • their BMI was 25.7 (overweight)

The researchers took a few measurements of the volunteers that included:

  • blood serum 25 OHD
  • height
  • weight
  • CT scan for:
    • abdominal subcutaneous fat (fat between the muscle and skin at the level of the belly button)
    • visceral fat (fat inside the abdomen at the level of the belly button)
    • thigh musculature and thigh fat (muscle and fat half way between the knee and hip of the thigh)
  • DXA of total fat

Results

To figure out whether Vitamin D levels were related to body fat distribution and fat in muscle, the researchers split  the women into two groups (Figure 1):

  1. Adequate levels of 25 OHD: Women with over 30 ng/ml of 25 OHD in their blood
  2. Inadequate levels of 25 OHD: Women with less than 29ng/ml
Figure 1 – Percent of women with adequate levels (>30 ng/ml) and inadequate levels (<29ng/ml) of Vitamin D (as figured out by serum 25 OHD).
Figure 1 – Percent of women with adequate levels (>30 ng/ml) and inadequate levels (<29ng/ml) of Vitamin D (as figured out by serum 25 OHD).

What were the differences between the women getting enough vitamin D and the women not getting enough?

Women not getting enough vitamin D were heavier, had more abdominal subcutaneous fat, had more visceral fat, had a greater BMI, more muscle fat and were shorter!

Surprised? I was.

There’s been a buzz about vitamin D and fat… but shorter? Yup, women with less vitamin D in their blood were shorter (on average) than the women with adequate levels of vitamin D.

Let’s take a closer look at the other findings.

Weight, BMI and Vitamin D

Women with adequate vitamin D were, on average, 7.4 kg (16.3 lb) lighter than women who didn’t have enough vitamin D.

That’s quite a bit, since the average weight was 68.3 (150.6 lb). If you do a relationship comparison (regression analysis), the more vitamin D (in the form of serum 25 OHD) a woman had the lighter she tended to be.

A woman with 35 ng/ml of 25 OHD in her blood is likely to be lighter than a women with 30 ng/ml, so not only is having enough vitamin D important, but more seems to be an advantage for lower body weight.

Women with inadequate levels of vitamin D have a triple whammy: Since they are heavier and shorter, they also have a higher BMI (weight /(height)2) The relationship between BMI and vitamin D levels was the same as with weight and vitamin D: the less vitamin D the higher the BMI . Figure 2 shows the differences in BMI between the two groups.

Figure 2 – BMI of women with adequate levels of blood vitamin D (25-OHD) and inadequate levels
Figure 2 – BMI of women with adequate levels of blood vitamin D (25-OHD) and inadequate levels

Abdominal fat, thigh muscle fat and Vitamin D

Lower levels of vitamin D meant more weight, but does it mean more fat or something else?

Off to the DXA scanner, Batman! You laugh, but I’m sure that guy has one — just look at all the toys.

Women without enough vitamin D had over 5.5 kg (12lb) more body fat (figure 3 below), but it gets worse, because of where this fat hangs out — around the abdomen both subcutaneously (between the skin and the muscle) and visceral (around the internal organs).

Women with inadequate vitamin D levels had 45% more visceral fat than women with adequate vitamin D levels (44.81 cm2 and 24.74 cm2 of visceral fat, respectively).

Holy! Forty-five percent more visceral fat, not good.

Figure 3– Body fat (kg) of women with adequate levels of blood vitamin D (25-OHD) and inadequate levels
Figure 3– Body fat (kg) of women with adequate levels of blood vitamin D (25-OHD) and inadequate levels

Why is this fat so bad? Visceral fat is particularly bad fat since it has been linked to high blood pressure, cardiovascular disease and type 2 diabetes. Take a look at one of my past reviews on abdominal fat.

Great, all the fat is accounted for! Right? Nope.

There is more fat… in the muscle. While more muscle fat (technically intramuscular fat) is great, say if you want a tasty, juicy T-bone steak, it’s not so hot if you want a functioning muscle.

As a percentage, women with inadequate vitamin D levels had 3.90% muscle fat compared to 3.15%. This is not a big difference (0.75%) but it’s enough to be considered different statistically.

Bone and vitamin D

You might be thinking, Hey, isn’t vitamin D involved in making bone? Yes it is, and they measured bone density using DXA.

Surprisingly, there was no difference in bone density between groups of women. Zippo, none, nada. Differences in height, weight, BMI, body fat, visceral fat and muscle fat, but no difference in bone density – go figure.

Conclusion

Women with inadequate amounts of vitamin D in their blood (25-OHD <29 ng/ml) were at higher risk of disease because they had more abdominal fat, both subcutaneous and visceral, more body fat and a higher BMI than women with adequate amount vitamin D. Not good.

A few surprises: inadequate amounts of vitamin D were related to being shorter and having more muscle fat, but made no difference in bone density.

Bottom line

This is another reason to make sure you get adequate amounts of vitamin D.

But before you go sunbathing all day , remember that if you’re light-skinned, your body makes 3,000 to 20,000 IU with a mere 10-15 minutes of midday sun exposure to the arms and legs. If your skin is darker, you’ll need 5-10 times more time.

If you’re stuck in a dark cave or winter in Edmonton, look into supplementing with 4,000 IU of vitamin D daily.

sunbathing
“Can I write this off as a medical expense?”

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