As the winter season progresses, many of us take extra precautions to ward off colds and flu. Recent research suggests that a straightforward and inexpensive vitamin D supplement might be the answer. This week, scientists from the universities of Surrey, Oxford, and Reading examined data from 36,000 British adults and discovered that those with significant vitamin D deficiencies were 33% more likely to be hospitalized for respiratory tract infections compared to those with adequate levels.
Sadly, vitamin D deficiency is common. The Department of Health and Social Care estimates that about one in six people in the UK have low vitamin D levels, a situation that worsens during the winter months due to decreased sunlight exposure, which limits our skin’s ability to produce this essential vitamin.
“Vitamin D is crucial for our physical health,” stated Abi Bournot, the study’s lead researcher from the University of Surrey. Beyond its role in supporting a robust immune system, increasing vitamin D levels can provide numerous other benefits for both body and mind.
It Can Lower the Risk of Colds, Flu, and Covid
Nicola Shubrook is the founder of Urban Wellness
CASSANDRA LANE
Vitamin D acts in a manner similar to hormones, acting as a messenger within the body, explains Nicola Shubrook, a nutritional therapist and founder of Urban Wellness. “It is activated by the liver and kidneys into calcitriol—the form that regulates hundreds of genes across various tissues, akin to oestrogen or cortisol.”
It stimulates vitamin D receptors (VDRs) found in numerous areas of the body, including the heart, bones, and lungs. When activated, these receptors enhance the production of antimicrobial proteins that help fend off infections. Furthermore, vitamin D improves the efficiency of immune cells, such as macrophages, which combat viruses and mitigate excessive inflammation that can exacerbate cold symptoms.
“Clinical trials indicate that a daily low dose can promote a robust immune response,” remarks Shubrook. A 2022 meta-analysis published in *Frontiers in Nutrition* found that individuals taking vitamin D supplements were 22% less likely to catch the flu compared to those who did not take them, while other studies have linked low vitamin D levels to a higher risk of severe Covid cases.
• Can vitamin D slow ageing? Here’s why I take it
Daily Intake of 10mcg is Advisable — No Need for High-End Brands
The NHS recommends that everyone should take a daily supplement of 10mcg (400IU) during the months of October to March. However, individual requirements may vary, according to Shubrook. “People with darker skin may find it more challenging to synthesize vitamin D naturally from sunlight. You can take supplements and still have low levels.”
Symptoms of deficiency can include muscle pain and feelings of low mood, but the only definitive way to determine your levels is through a blood test. This can be arranged through your GP or via a private at-home finger prick test. The NHS defines deficiency as levels below 25 nmol/l of calcidiol in the blood, while a level of 50 nmol/l is considered sufficient. If found deficient, 25mcg (1,000 IU) supplements are widely available. The NHS advises that the upper limit of vitamin D intake for most adults and children over 11 is 100mcg (4,000 IU) per day. The primary (though rare) side effect of excessive intake is hypercalcemia, which can lead to symptoms like nausea and kidney stones.
In addition to pills, there are also sprays and drops for sublingual use available (e.g., BetterYou Vitamin D 3000 IU (75 mcg) Daily Oral Spray, £10.40, boots.com). Evidence suggests all forms are equally effective, but as a fat-soluble vitamin, “any vitamin D supplement should ideally be consumed with a meal containing fat for the best absorption,” states Shubrook. She believes there’s no justification for purchasing expensive brands. “I use a reasonably priced brand.” For instance, Superdrug’s 25mcg tablets are £3.99 for 90, while Boots’ in-house brand offers 180 10mcg tablets for £4.
• Read more expert advice on healthy living, fitness, and wellbeing
Combine it with Calcium for Enhanced Bone Strength
Vitamin D, found in oily fish like salmon, helps your body absorb calcium from food.
GETTY IMAGES
Vitamin D “enhances the absorption of calcium from your diet and facilitates transport to the bones, where it aids in the formation of osteoblasts,” explains Shubrook. Nevertheless, certain studies suggest it is most effective for strengthening bones when paired with a calcium supplement. A meta-analysis published in the *JAMA Network* revealed that daily supplementation of 10–20mcg of vitamin D along with 1,000–1,200mg of calcium resulted in a 16% reduced risk of hip fractures (e.g., Vitabiotic Ultra Calcium tablets blend 20mcg of vitamin D with 1,000mg of calcium for £3.65 for 30, vitabiotics.com).
Shubrook recommends that the elderly and individuals at risk for heart disease consider taking vitamin K along with vitamin D, as it prevents calcium from accumulating in the walls of blood vessels, thus maintaining their flexibility.
• How to get vitamin D in winter—and how much you really need
Vitamin D’s Role in Mood Enhancement
“Vitamin D influences the production of neurotransmitters such as serotonin and dopamine, which are crucial for mood regulation,” explains Shubrook. “Insufficient levels can contribute to seasonal affective disorder.”
Natalie MacKenzie, a cognitive rehabilitation therapist, notes that VDRs are “highly concentrated in key areas of the brain, including the hippocampus and prefrontal cortex. These receptors allow vitamin D to directly affect neuron development and communication, ultimately influencing cognitive health and function.”
Additionally, vitamin D reduces inflammation, “a known contributor to cognitive decline linked to conditions such as Alzheimer’s disease,” states MacKenzie. “Numerous large-scale observational studies and meta-analyses reveal strong links between low vitamin D levels and an increased risk of dementia and cognitive impairment.”
Boosting Muscle Strength and Energy
Vitamin D activates VDR receptors in muscle cells, which helps regulate muscle growth. A meta-analysis published in the *Journal of the American Geriatrics Society* discovered that daily supplementation of 17–25mcg significantly enhanced muscle strength, particularly among individuals with low baseline levels. The vitamin also plays a vital role in calcium regulation within muscles, essential for proper contraction and relaxation, and enhances mitochondrial function, which is responsible for energy production.
Research within older populations has indicated an inverse relationship between vitamin D levels and fall risk, while a meta-analysis of studies involving young adults published in the *Journal of Science and Medicine in Sport* found that vitamin D supplementation “markedly increased muscle strength in both upper and lower limbs compared to control groups.” However, it was noted that benefits were more pronounced among participants who started with lower levels.
Increase Vitamin D Potency in Mushrooms by Sunlight
Mushrooms provide vitamin D too, and placing them on a sunny windowsill can enhance their levels.
GETTY IMAGES
While it can be “challenging” to obtain adequate vitamin D through diet alone, Shubrook notes that good sources include oily fish like salmon and sardines, as well as tinned tuna and eggs. She also mentions that mushrooms can be good sources of vitamin D, with their levels increasing if left on a sunny windowsill, as they contain ergosterol which converts to vitamin D2 with UV light interaction, similar to how human skin produces vitamin D3 from the sun.
Foods such as cereals, cow’s milk, and plant-based milks are often fortified with vitamin D, which Shubrook advocates for, considering its importance during the winter when obtaining sufficient levels can be difficult.
