AAs winter sets in and Australians living in southern states wear scarves, beanies and puffer jackets, many brace for a cold and flu season. Being a season that also tends to bring less sun exposure, winter is associated with lower vitamin D levels, which our body gets mainly from the sun. And while this is known to impact bone health, there is growing evidence that vitamin D functions could be more extensive, with deficiencies linked to an increased risk of respiratory infections.
“When our vitamin D levels are extremely low, it can cause muscle aches and body aches and can impact the immune response to infections,” says Vicki Kotsirilos, associate professor at Western Sydney University. “As we head into winter, this is an important consideration.”
What is Vitamin D?
Despite its common name, fat-soluble vitamin D is now considered a hormone. It is made by the body through a series of steps. When exposed to ultraviolet B (UVB) rays from the sun, cholesterol in the skin is converted into cholecalciferol (D3) and ergocalciferol (D2), which travel through the blood to the liver where they are metabolized to form calcidiol. These then travel to the kidneys and are converted into the active hormone, calcitriol.
About 90% of our vitamin D intake comes from the sun. “Vitamin D deficiency is sunlight deficiency,” says Ian Brighthope, professor of nutritional and environmental medicine and director of the National Institute of Integrative Medicine.
We can get smaller amounts from food in the form of vitamin D3 or D2. Food sources include fatty fish such as salmon and tuna, eggs, mushrooms, beef liver and whole milk. Supplements are also a source of vitamin D3.
Vitamin D and the immune system
Vitamin D helps bones absorb calcium and other important minerals and has long been known to help prevent rickets in children and bone problems such as osteoporosis in adults. But it became clear that the impact of vitamin D went far beyond bone health after the discovery of vitamin D receptors in most body cells – including immune cells – signaling other functions.
“Vitamin D has a very broad spectrum of activity,” says Brighthope. “Probably its most important activity is in the immune system, because we now know that people who have high levels of vitamin D in their system are less likely to get acute and serious respiratory infections and end up in hospital. and die in intensive care.”
There is a general consensus on the importance of sun exposure, but Professor Prue Hart, senior researcher at the Telethon Kids Institute, suggests that the benefits are not due to vitamin D but rather to other molecules produced by the skin. Hart says that although vitamin D blood levels are associated with immunity, clinical trials of supplementation have shown no benefit.
While some studies have showed no benefita 2017 meta-analysis of 25 randomized controlled trials with over 11,000 participants reported that vitamin D supplements helped prevent acute respiratory infections.
As these different studies suggest, nothing is simple, because several factors could be at play in respiratory infections. Vitamin D supplements are most likely to benefit someone with a deficiency.
“Vitamin D is just one member of an orchestra of nutrients and it doesn’t work very well if you abuse your kidneys and liver with alcohol or if you eat high levels of salt, fat and sugar in particular,” says Brighthope. “All of these things suppress your immunity.” Vitamin D supplements may not always work in people with comorbidities such as heart disease, cancer, stroke, diabetes and metabolic syndrome, he adds.
Brighthope says a doctor with a degree in nutrition is best equipped to deal with these complexities.
How do you know if you are deficient?
Rickets or osteoporosis could be red flags for vitamin D deficiency, as could muscle aches and pains, as Kotsirilos noted. Other than that, it’s hard to say.
“Vitamin D deficiency doesn’t come with too many symptoms,” says Brighthope. People may notice neuropsychiatric or neurophysiological changes, he notes. “For example, it can be fatigue, lack of sleep, lack of appetite, depression, or depression mixed with anxiety.” But all this could also be attributed to other factors.
Therefore, a blood test is the best way to measure vitamin D status.
Who is at risk?
People who live in the lower latitudes of Victoria, ACT, New South Wales, South Australia and Tasmania are generally at greater risk of deficiency than those in northern regions.
“There are also what we call subpopulations within these groups that are at high risk for vitamin D deficiency,” Kotsirilos says. “For example, people who are more housebound, people living in the community, the elderly and/or disabled, people with dark skin, and people who are overdressed and avoid the sun or work indoors. ” Sunscreen can also block UVB rays.
How can I increase my vitamin D level?
Getting outside is the best way to boost vitamin D levels. “The easiest way is to be safe in the sun,” says Kotsirilos. But with our modern lifestyles, this can be tricky.
“We were meant to live in daylight,” says Brighthope. “We weren’t supposed to live in caves, but I’m sure you’re sitting in your cave right now, like me. So you really should be out there looking for nuts, seeds, berries, and maybe doing a little fishing. Physical activity is also thought to help the body produce vitamin D.
Failing that, supplementation can help boost low vitamin D levels. Recommended intakes vary widely, and it’s best to consult a doctor for proper supplement dosage and monitoring.
What about the risk of skin cancer?
Australians have a relatively high rate incidence of skin cancerusually from excessive UV exposure, so common sense should prevail when stepping out in the sun.
“Going out in the midday sun in the summer is crazy, and going to ultraviolet tubs to tan is crazy,” says Brighthope. Basically, Hart says we should avoid sunburn – but it’s usually not such a big deal in the winter.
“During the summer, it is important to cover up and be safe between 11 a.m. and 5 p.m.,” says Kotsirilos. In balance with vitamin D needs, sun protection is recommended if the the UV index is greater than 3.
Brighthope suggests exposing your skin to a moderate amount of sunlight for 20 minutes a day or up to 30-60 minutes before 11 a.m. and after 3 p.m. “Provided you are not fair-skinned,” he adds. For very pale people, Kotsirilos offers 15 minutes of exposure per day. “It’s a matter of knowing yourself and knowing everything in moderation.”