The study – published in the Journal of Leukocyte Biology – reports that intake of vitamin D supplements during autumn and winter months could help to protect against viral infections, especially in older people.
Led by Dr Victor Manuel Martinez-Taboada from the Unversidad de Cantabria, Spain, the research team explained that levels of vitamin D – otherwise known as the sunshine vitamin – decrease during autumn and winter when days are shorter and sunlight is relatively weak. They suggest this could explain why people are more prone to viral infection during these times, arguing that supplementation, especially in older populations, could strengthen people's innate immunity against viral infections.
"There are numerous studies showing the benefits of maintaining adequate Vitamin D levels. As more and more research into Vitamin D is conducted, we are learning that it is extremely important for human health,” said Martinez-Taboada.
"Our study is no different, and vitamin D supplements should be considered one of many tools that might help when conventional therapies are not enough," he added.
Commenting on the research, Dr John Wherry, deputy editor of the Journal of Leukocyte Biology noted: "There have been numerous studies showing several environmental factors during winter months may allow viruses to spread easier ... This study shows that sunlight, or more precisely the lack of vitamin D, could have a role in the seasonally higher rates of infection.”
Wherry added that further and ‘more extensive’ studies must be conducted before any association can conclusively be shown. However he conceded that because vitamin D supplements are inexpensive and generally safe: “this is a really exciting discovery."
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D).
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 and -2 diabetes.
In the new study, Martinez-Taboada and his colleagues compared the changes in the blood levels of vitamin D among three groups of healthy subjects: young (age range: 20-30), middle (age range: 31-59), and elderly (age range: 60-86).
They found decreased levels of vitamin D with aging, prompting researchers to compare whether such changes kept any relationship with the expression of key immune markers – such as toll-like receptor (TLR) expression measured on lymphocytes and monocytes.
The study revealed that the TRL most affected by a vitamin D insufficiency is TLR7 – which regulates the immune response against viruses.
Source: Journal of Leukocyte Biology
Volume 91, Number 5, Pages 829-838, doi: 10.1189/jlb.1011523
"Age and low levels of circulating vitamin D are associated with impaired innate immune function"
Authors: Lorena Alvarez-Rodriguez, Marcos Lopez-Hoyos, Maite Garcia-Unzueta, Jose Antonio Amado, et al