Everyone knows that vitamin D helps to absorb calcium.
What is less known is that it affects muscle as well — and in a positive way.
Low levels of vitamin D leads to sarcopenia, a Medical–Greek word that literally means “muscle deficiency.”
Studies confirmed this, both in Korea and in The Netherlands.
Researchers examined over three thousand Koreans in this study.
And they defined sarcopenia as a very low muscle-weight to body-weight ratio.
They found a strong correlation between circulating vitamin D levels and low muscle mass.
The chemical name for vitamin D is 25-(OH)D₃, and this chart shows you the correlation they found.
Our data suggest that vitamin D deficiency was associated with an increased risk of having sarcopenia in older Koreans.
This finding may be news to some, but it’s not surprising to many biochemists and doctors.
In fact, there have been published case reports for decades.
Dr. Prabhala describes five cases in which vitamin D myopathy became so severe that wheelchairs were necessary.
Myopathy is a Medico-Greek word meaning “muscle suffering.”
In all cases, this was reversible with vitamin D.
Outside his home, he used a wheelchair. His weakness and bone pains resolved within 6 weeks. He currently walks 2 to 3 blocks on his own without support.
What can cause vitamin D deficiency to this degree? One thing is a lack of sun exposure.
And these severe cases can happen especially in northern states, like New York, where sun exposure is low.
But milder forms of weakness can happen anywhere among civilized people who spend too much time indoors.
The good news is that you can take vitamins for weak muscles by taking vitamin D supplements.
For those who don’t use UV light, they can buy pills that range from 400 IU all the way up to 50,000 IU.
So what vitamin D dosage is a good amount to take?
Researchers found doses of 5,000 IU effective in increasing muscle strength in a group of forty-year-old subjects.
They recruited thirty subjects and split them into two groups: one on 2,000 IU and one on 5,000 IU.
The researchers measured the volunteers’ muscle strength with a dynamometer at the start and again at different times.
And they found significant increases in strength in both groups.
But the high vitamin D group reported higher strength.
Now, when there is not enough vitamin D or calcium available, the body will take calcium from the bones.
The body increases parathyroid hormone to pull the calcium from the bones.
Since they increased the volunteers’ vitamin D, the researchers expected parathyroid hormone to decrease.
And they were not disappointed:
These dosages are safe and effective and result in improvements in parathyroid hormone activity and muscle strength.
There are many reports written on how this works.
Stanley Birge did experiments in which he found that vitamin D increased phosphate into the muscle.
It also increased muscle protein synthesis, as measured by radiolabeled leucine uptake.
He found a muscle receptor that had a very high binding affinity for vitamin D.
Vitamin D also increased ATP levels, a molecule necessary for muscle contraction.
He found that only the 25-(OH)D₃ metabolite works to increase phosphate and ATP.
But other researchers found that 1α,25-(OH)D₃ works on muscle too, by increasing calcium.
Calcium is also necessary for muscle contraction.
vitamin D repletion alters muscle metabolism, resulting in increased ATP concentrations and accelerated incorporation of an amino acid into muscle protein.
This translates to increased strength.
Specifically, it translates into increased type II muscle fibers — type II muscle fibers are the fast-twitch type.
Yoshihiro Sato gave 96 older subjects 1,000 IU for two years.
Then he took a muscle biopsy so he could measure the muscle fiber directly under a microscope.
Besides noticing an increase in strength, he found more type II muscle fibers in the vitamin D group.
And the fibers also had a larger diameter.
Dr. Sørensen of Denmark demonstrated this as well in 1978.
He gave patients the most active form of vitamin D, 1α,25-(OH)D₃, for 3–6 months.
He found increased type II fibers, ATP, and creatine.
He also measured the cell’s ability to utilize carbohydrate and noticed increased metabolism in the vitamin D group.
As well as enhancing the oxidative capacity, 1α,25-(OH)D₃, also increased the ATP and creatine phosphate stores of the muscle cell.
Vitamin D is a major determinant of muscle strength, though most people don’t know it.
Probably because it’s free (from the sun!) and nobody can sell it to you.
If you don’t want to go tanning, the effective dose is usually 5,000 IU, but lean people can do with less (~2,000 IU).
This is almost ALWAYS safe.
In fact, only one person in a few thousand is hypersensitive and should be taking less (~800 IU).
Severe Myopathy Associated With Vitamin D Deficiency in Western New York
Effect of oral cholecalciferol 2,000 versus 5,000 IU on serum vitamin D, PTH, bone and muscle strength in patients with vitamin D deficiency
25-Hydroxycholecalciferol Stimulation of Muscle Metabolism
Role of Vitamin D in Skeletal Muscle Function