A new study showed that increased vitamin D intake can help to prevent age-related diseases, in particular loss of vision and blindness.
The researchers found that middle-aged mice treated with the vitamin for six weeks had lower levels of a toxic protein linked to age-related macular degeneration, heart disease and Alzheimer's. The study adds to growing evidence linking vitamin D, naturally generated by ultraviolet rays from the sun on skin, with a diverse range of disorders including diabetes, arthritis and some cancers. They reported their findings in the journal Neurobiology of Aging. AMD is the leading cause of blindness among people over 50 in the developed world.
Lower levels of amyloid beta in the mice's eyes and blood vessels led to significant improvement in their vision. Vitamin D treatment also reduced numbers of cells called macrophages, which play a vital role in the immune system and can also trigger inflammation. The accumulation of these proteins and inflammation can increase the risk of people developing age-related macular degeneration. However, the researchers did not specifically look at a mouse model of AMD and this study has limited relevance to humans. Therefore, it’s not possible to say, based on the study’s results, whether vitamin D has any effect on age-related vision loss or AMD in humans.
Seven 12-month-old female mice were injected with vitamin D and safflower oil under their skin every three days for six weeks. A control group was injected with safflower oil only, at the same frequency. Before treatment, the researchers recorded how well the mice’s eyes responded to visual stimuli by recording the electrical signals made by the retina cells when the mice were exposed to flashing lights. After the treatment, the researchers dissected the mice’s eyes and stained them for a protein, amyloid beta, which accumulates with ageing. They also stained for a protein called C3d, which is a marker of inflammation. Finally, they counted the number of inflammatory cells (macrophages) in and around the retina and looked at their shape, which shows whether these cells were active or not.
After the treatment period there were significant differences in how mice’s retinas responded to stimuli between the control and treated mice. The researchers found that in the eyes of the vitamin D-treated group of mice there were fewer macrophage cells, and their shape suggested that they were less active in terms of causing inflammation. The mice treated with vitamin D had less build-up of the protein amyloid beta in their eyes than the control mice. The control mice experienced more inflammation, as judged by looking at the amount and form of the inflammation marker C3d. After the treatment period, there were significant differences in how mice’s retinas responded to stimuli between the control and treated mice.
Professor Glen Jeffrey of UCL's Institute of Opthalmology, who led the research, explained that tiny blood vessels that supplied the retinas became clogged with debris over time, while they also became inflamed. Both processes narrowed them. “In humans this can result in a decline of up to 30 per cent in the numbers of light receptive cells in the eye by the time we are 70 and so lead to poorer vision,” he said.
Jeffrey, professor of neuroscience, cautioned, “Researchers need to run full clinical trials in humans before we can say confidently that older people should start taking vitamin D supplements.” That warning was echoed by Clara Eaglen from the RNIB. “It is important to remind people that this is a trial,” she said. “Anyone thinking about taking a vitamin supplements should consult their doctor. Taking high levels of supplements can cause other health problems.”
A spokesman for the Macular Disease Society said the study “will contribute to overcoming what is the most common cause of sight loss in the UK”.
The study was funded by the Biotechnology and Biological Sciences Research Council (BBSRC). Professor Douglas Kell, chief executive of the Biotechnology and Biological Sciences Research Council, said, “Many people are living to an unprecedented old age in the developed world. All too often though, a long life does not mean a healthy one and the lives of many older people are blighted by ill health as parts of their bodies start to malfunction. If we are to have any hope of ensuring that more people can enjoy a healthy, productive retirement then we must learn more about the changes that take place as animals age. This research shows how close study of one part of the body can lead scientists to discover new knowledge that is more widely applicable. By studying the fundamental biology of one organ scientists can begin to draw links between a number of diseases in the hope of developing preventive strategies.”