Vitamin D plays an important role in regulating the body's absorption of calcium and phosphorus, as well as keeping the brain and immune system functioning.
And now researchers from UFSCar (Federal University of São Carlos) and University College London (United Kingdom) have shown that the substance also reduces the risk of muscle weakness by 78% —a condition that in medical jargon is called dynapenia.
This weakness can be partially explained by muscle atrophy and is considered an important risk factor for physical disability in aging. People with dynapenia have a higher incidence of falls, hospitalization, early institutionalization and premature death.
In the study, published in the journal Calcified Tissue International and Musculoskeletal Research, researchers analyzed 3,205 Britons aged over 50 who were followed for four years as part of the English Longitudinal Study of Aging (ELSA) project. The work was supported by FAPESP.
“It is known that vitamin D participates in several functions in the body. It is actually a hormone and among its various actions is muscle repair and also the release of calcium to contract the muscle [cinética da contração muscular] Therefore, it was already expected that vitamin D would cause some muscle alteration and that is exactly what our study proved”, says Tiago da Silva Alexandre, professor of the department of gerontology at UFSCar and research advisor.
The scientist explains that bone and muscle tissues are interconnected not only mechanically and physically, but also biochemically.
“For this reason, endocrine disorders, such as vitamin D deficiency and insufficiency, favor the loss of bone mineral density, as well as the decrease in muscle mass, strength and function”, he says.
In the study, the researchers selected individuals over 50 years of age who did not have muscle weakness, that is, they had neuromuscular strength greater than or equal to 26 kg for men and greater than or equal to 16 kg for women. This measurement is made with a device that measures handgrip strength, which has a good correlation with the body's overall strength.
By following the participants for four years, the researchers found that those who had vitamin D deficiency at the beginning of the study (blood level less than 30 nanomol per liter) had a 70% greater risk of developing muscle weakness at the end of the study than those who had normal vitamin D levels (blood level greater than 50 nmol/l).
“This is already an important finding, as it shows that vitamin D deficiency increases the risk of muscle weakness by 70%. However, as we know that there are many cases of people with osteoporosis worldwide who take vitamin supplements, we needed to check what would be the weight of the supplementation”, says Maicon Luís Bicigo Delinocente, FAPESP scholarship holder and co-author of the study.
To this end, the researchers excluded individuals who had osteoporosis and were taking vitamin D supplementation from the analysis.
“When these individuals were removed from the analyses, it was found that those who had vitamin D deficiency at the beginning of the study had a 78% greater risk of developing muscle weakness. [nível no sangue entre 30 e 50 nmol/l] showed a 77% greater risk of developing weakness at the end of the four years of follow-up when compared to those who had normal levels of vitamin D”, says Delinocente.
Alexandre points out that, with the result, it was possible to prove that not only the deficiency, but also the insufficiency of vitamin D make the individual have a greater risk of developing muscle weakness.
“Another reflection of the study's findings is the importance of vitamin D replacement, when necessary. The study was carried out with British people and we know that the solar incidence in Brazil is much higher than in Great Britain, but the fact is that we also have a high incidence of deficiency and insufficiency of vitamin D in Brazil and in the world, mainly among older individuals”, he says.
Alexandre reiterates that, for the synthesis of vitamin D to occur in the body, it is necessary to sunbathe with exposed areas of the body.
“But it is necessary to explain to people that vitamin D insufficiency and deficiency increase the risk of developing loss of muscle strength. Therefore, it is necessary to say that these people need to be more exposed to the sun, follow a diet with foods rich in vitamin D or do supplementation and practice resistance exercise to maintain strength”, he concludes.