Vitamin D for improved cardiorespiratory fitness and strength

Posted by Dayne Hudson in Wellness

Estimated reading time: 6mins

Vitamin D for better 1RMs and fitness?

Heads have turned everywhere in the health and fitness science circle, with this fresh study into 74 men and women volunteer twins.

Firstly, twins are great for scientists to study because there are far fewer variables; studying identical twins means results can better determine whether a certain trait, illness, or disorder is influenced more heavily by genetics or by the environment.

The twins in this randomised control trial were aged between 18–40 years (mean age of 25 years) and consumed one oily capsule of cholecalciferol (vitamin D) per day, with a concentration of 2,000 IU, for a period of 60 days, in the morning.

They tested hand strength and scapula strength with the following:

"The scapular dynamometer that measured scapula strength."

Each study participant stood up and held the dynamometer at chest level, without it touching the chest.

With their elbows open and parallel to the ground, they performed a maximum scapular contraction lasting 3–5 seconds, with three repetitions, and 60 seconds of rest. The highest value between attempts went down as the final result.

The other way strength was tested was with a hand grip:

"Jamar Hand Dynamometer"

They performed 5 seconds of maximum contraction in each handgrip and rested for 60 seconds in between the measurements.

To test their fitness, a treadmill was utilised to decipher their absolute and relative VO2max in a test period of 8–12 min (in line with current recommendations).

So what did they find?

Their cardiorespiratory fitness improved through increases in the values of maximum oxygen consumption of 28%. Moreover, muscle strength in the left hand increased by 18%. The researchers concluded:

"Sixty days of cholecalciferol supplementation improved cardiorespiratory fitness and upper limb muscle strength."

Improved cardiorespiratory fitness and upper limb muscle strength.

Vitamin D for our health and gym results

This is a key finding for fitness science, as although there has been evidence to say vitamin D is important for VO2max, a lot of those studies have been observational.

But this new study is, of course, cause and effect evidence; and even better given it was a randomised controlled trial and done into twins!

This is further to what science has found in vitamin D; its important role in immunity and in heart and muscle functioning.

We have vitamin D receptors in our muscle cells, heart muscle and vascular smooth muscle (the major cells in the media layer of arteries), and so it's not surprising that vitamin D deficiencies are related to:

  • Muscle weakness
  • Arterial thickening,
  • Myocardial hypertrophy (enlarged heart)
  • Hypertension. 

Getting enough vitamin D

It stands to reason based on all of this, that getting enough vitamin D is not only important for your strength and fitness but your health, too.

And us Aussies are guilty of not getting enough.

Research shows an estimated 31% of Australian adults don't get enough vitamin D and more than 50% of women in the southern states in southern states during winter and spring.

It's obviously tougher to get vitamin D in the colder months, and sometimes we don't get enough time to simply get outside and get some sunshine.

And eating enough vitamin D can be difficult too, as scientists put it:

"Vitamin D is found naturally in only very few foods."

So where can we get vitamin D from food? Here are our options:

  • Fish
  • Mushrooms
  • Pork, Beef, Chicken, Eggs
  • Butter, cheese
  • Cereals (corn flakes)
  • Orange juice
  • Milk

And for vegans and vegetarians, their options are rather limited; mushrooms and some cereals are a good bet.

And so this is why supplements exist; to plug this hole that needs immediate attention.

So, Bulk Nutrition have you covered with their Bulk Nutrients Proviotic supplement, which contains 5 micrograms of Vitamin D. Meanwhile, their Vital Pre Mix contains approximately the same.

Get a healthy dose of Vitamin D despite the weather with our Proviotic.
Get a healthy dose of Vitamin D despite the weather with our Proviotic.

The aforementioned study used 50 micrograms of vitamin D, but the another way to increase your vitamin D intake is to simply go outside.

This study found that it was possible for fair-skinned individuals to obtain 1000 IU of vitamin D within 30 min of exposure of 11% or 17% of skin to the sun. But it's critical we do this outside of the high UV periods of 10 am to 3 pm.

For a more precise prescription, the excellent table below shows how many minutes at what time of the day you can achieve 1000 IU of vitamin D!

"3 Duration (min) required to achieve synthesis of 1000 IU of vitamin D with one side of the hands, arms, neck and lower legs (17% of the body) exposed to the sun (0.294 MED), by city, season and time of day*"

The bottom line for Vitamin D

Is this fresh study carried out with great diligence, shows that vitamin D improves cardiorespiratory fitness and strength. The fact it was done into twins adds further weight to this rather important finding! Vitamin D can be obtained from a supplement, a limited variety of food, or by going outside. A lack of vitamin D is associated with muscle weakness, arterial thickening, myocardial hypertrophy (enlarged heart), and hypertension. Whereas getting enough is great for immunity, heart and muscle functioning.


  • Medeiros JFP, Borges MVO, Soares AA, de Sousa EC, Costa JRRD, Silva WAC, de Sousa MVB, Silbiger VN, Dantas PMS, Luchessi AD. Association of Vitamin D Supplementation in Cardiorespiratory Fitness and Muscle Strength in Adult Twins: A Randomized Controlled Trial. Int J Sport NutrExercMetab. 2021 Oct 23:1-6. doi: 10.1123/ijsnem.2021-0060. Epub ahead of print. PMID: 34689128.
  • Sahu M, Prasuna JG. Twin Studies: A Unique Epidemiological Tool. Indian J Community Med. 2016;41(3):177-182. doi:10.4103/0970-0218.183593
  • Guazzi, M., Arena, R., Halle, M., Piepoli, M.F., Myers, J., & Lavie, C.J. (2016). Focused update: Clinical recommendations for cardiopulmonary exercise testing data assessment in specific patient populations. European Heart Journal, 133, 694–711.
  • Autier, P., Boniol, M., Pizot, C., & Mullie, P. (2014). Vitamin D status and ill health: A systematic review. Lancet Diabetes & Endocrinology, 2(1), 76–89.
  • Todd, J.J., Pourshahidi, L.K., McSorley, E.M., Madigan, S.M., & Magee, P.J. (2015). Vitamin D: Recent advances and implications for athletes. Sports Medicine, 45(2):213–229.
  • Bouillon, R., Carmeliet, G., Verlinden, L., Van Etten, E., Verstuyf, A., Luderer, H.F., & Demay, M. (2008). Vitamin D and human health: Lessons from vitamin D receptor null mice. Endocrine Reviews, 29(6), 726–776.
  • Beaudart, C., Buckinx, F., Rabenda, V., Gillain, S., Cavalier, E., Slomian, J., Petermans, J., Reginster, J-Y., & Bruyère, O. (2014). The effects of vitamin D on skeletal muscle strength, muscle mass, and muscle power: A systematic review and meta-analysis of randomized controlled trials. Journal of Clinical Endocrinology & Metabolism, 99(11):4336–4345.
  • Pitz, S., März, W., Wellnitz, B., Seelhorst, U., & Fahrleitner Pammer, A. (2008). Association of vitamin D deficiency with heart failure and sudden cardiac death in a large cross-sectional study of patients referred for coronary angiography. Journal of Clinical Endocrinology & Metabolism, 93(10), 3927–3935.
  • Daly RM, Gagnon C, Lu ZX, Magliano DJ, Dunstan DW, Sikaris KA, Zimmet PZ, Ebeling PR, Shaw JE. Prevalence of vitamin D deficiency and its determinants in Australian adults aged 25 years and older: a national, population-based study. Clin Endocrinol (Oxf). 2012 Jul;77(1):26-35. doi: 10.1111/j.1365-2265.2011.04320.x. PMID: 22168576.
  • Bendik I, Friedel A, Roos FF, Weber P, Eggersdorfer M. Vitamin D: a critical and essential micronutrient for human health. Front Physiol. 2014;5:248. Published 2014 Jul 11. doi:10.3389/fphys.2014.00248
  • Stalgis-Bilinski KL, Boyages J, Salisbury EL, Dunstan CR, Henderson SI, Talbot PL. Burning daylight: balancing vitamin D requirements with sensible sun exposure. Med J Aust. 2011 Apr 4;194(7):345-8. doi: 10.5694/j.1326-5377.2011.tb03003.x. PMID: 21470084.

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