While we know that vitamin D is crucial for our immune system, a new study suggests that its powers extend far further. Researchers in the United States have found that giving heart attack patients a targeted dose of vitamin D may cut in half the risk of their having a second heart attack.
Dr Heidi May, a cardiovascular epidemiologist at Intermountain Health in Salt Lake City and the study’s lead investigator, said the results were promising and that her team “observed no adverse outcomes when giving patients higher doses of vitamin D3 supplementation”.
The “sunshine vitamin” is so called because it is produced in the skin during sun exposure; however, many of us are not getting enough of it. Living in Britain, where a full day of sunshine is a rare occurrence during the winter months, this perhaps should not be a surprise.
Many of us turn to supplements or dietary tweaks to ensure we are getting enough of the crucial vitamin. In fact, it is the one food supplement that the NHS recommends we take during the autumn and winter months – and yet, 50 per cent of UK adults have lower than “optimal” levels.
So, what are the benefits of vitamin D, how much of it do we need, and who is most at risk of deficiency?
1. Good for the heart
Scientists have consistently linked low levels of vitamin D to poor cardiovascular outcomes. However, previous studies struggled to show that a standard dose of vitamin D reduced the risk of cardiovascular disease.
Now, researchers at Intermountain Health have found that giving heart attack patients a targeted dose of vitamin D3 slashes their risk of another heart attack by 50 per cent. Rather than giving everyone a standard dose, the researchers adjusted supplementation to ensure that each patient reached optimal levels of vitamin D in their blood.
“The link between the health of the blood supply to the body – including the heart and vitamin D levels – and to the brain has long been studied,” says David Llewellyn, a professor of clinical epidemiology and digital health at the University of Exeter Medical School.
“Researchers have hoped that improving vitamin D levels might not just protect against heart disease, but a range of vascular problems, including stroke.” A wide-ranging review in Nutrients investigated this link and noted that vitamin D may help to prevent cardiovascular disease and improve outcomes for stroke patients, although more wide-ranging research is needed.
2. Boosts cognitive function
Taking vitamin D supplements could protect your brain against dementia and cognitive decline, Prof Llewellyn says. He references a large study in the US where researchers followed more than 1,600 people and discovered that those with a mild vitamin D deficiency were around 53 per cent more likely to develop dementia of any type and 69 per cent more likely to develop Alzheimer’s disease. Those with a severe deficiency were more than twice as likely to develop dementia or Alzheimer’s.
In a recent study, Prof Llewellyn and his team investigated the risk factors for early onset dementia, compiling data from more than 350,000 people in the UK Biobank. They found that “even in younger adults (people in their 40s and 50s), when they developed dementia, vitamin D deficiency was a substantial risk factor alongside a range of other things that influence brain health” such as alcohol use disorder and hearing impairment.
“We know that vitamin D crosses over the blood-brain barrier into the brain and we also know that there are receptors for vitamin D across the brain, which implies it has an important function,” Prof Llewellyn explains. Research suggests that vitamin D reduces inflammation in the brain, helps to protect against oxidative stress and may help to break down and clear protein deposits linked to Alzheimer’s disease.
3. Strengthens the bones
One of vitamin D’s more well-known roles is supporting the health of our bones and teeth as it helps to regulate the amount of calcium in the body.
“Vitamin D as calcitriol [its biologically active form] increases the absorption of calcium and phosphate. This helps to maintain normal serum calcium levels, which is essential for bone mineralisation,” explains Dr Roger Henderson, a leading GP and a spokesman for Olbas Oil.
“Without vitamin D you get rickets in children or osteomalacia in adults,” he says, adding that adequate intake supports fracture prevention in older people and those with a deficiency. This was demonstrated in a 2022 study which concluded that patients with vitamin D deficiency showed a significant risk reduction of falls after supplementation.
4. Improves oral health
Several studies have found an association between low vitamin D levels and worse dental health, Dr Henderson says. He points to a systematic review which linked a vitamin D deficiency to a higher risk of tooth decay (especially in children), impaired tooth mineralisation, and possibly poorer implant and wound healing. Plus, research in 2020 linked lower vitamin D levels with an increased risk of periodontitis (a serious gum infection), possibly because of its connection to the immune system.
We know that vitamin D aids “calcium and phosphate metabolism”, which is important for strong teeth, plus it has “anti-inflammatory and antimicrobial effects in oral tissues” which may help to fight infections, Dr Henderson explains.
5. Strengthens muscles
Vitamin D supplementation may help some older adults improve their muscle strength, Dr Henderson says, pointing to a 2023 meta-analysis which found it was most effective for those with a deficiency.
Plus, a 2022 study found that a vitamin D deficiency greatly increases a person’s chance of age-related loss of muscle strength (dynapenia), a major risk factor for falls. Researchers analysed data from more than 3,200 people aged 50-plus and found that those deficient in vitamin D were 70 per cent more likely to develop dynapenia by the end of the study than those with normal levels.
The results make sense, the researchers said, since vitamin D is known to help with muscle repair and contraction by transporting calcium and reducing inflammation.
“However, some well-designed trials show no effect in vitamin-replete or younger populations,” Dr Henderson warns.
How much vitamin D do we need each day?
Most adults and children over five in the UK need 10 micrograms (400 IU) of vitamin D each day, Dr Henderson says. From October to March, the NHS recommends we take a daily supplement to ensure we get enough of it.
What about those at higher risk of vitamin D deficiency?
Older adults
10mcg a day. “Older people are at a higher risk of deficiency and may particularly benefit from supplementation to support bone and muscle health,” Dr Henderson says.
Pregnant and breastfeeding women
10mcg a day. Those at a higher risk (with darker skin, limited sun exposure, or obesity) may be recommended a higher dose, Dr Henderson says.
People who are housebound/have limited sun exposure
10mcg a day, with supplements recommended all year round.
People with dark skin
African, Afro-Caribbean and some people with south Asian backgrounds are advised to take 10mcg a day in supplement form, all year round, “since less cutaneous vitamin D is produced from the same sunlight exposure,” Dr Henderson explains.
FAQs
What is a safe amount of vitamin D to take every day?
The NHS advice is not to take more than 100mcg (4,000 IU) of vitamin D per day as this could be harmful for adults. Upper limits for children are lower.
“Excess vitamin D can cause hypercalcaemia, with symptoms including nausea, weakness, kidney stones, and cardiac conduction problems,” Dr Henderson says. “That’s why high pharmacological doses should be supervised and blood calcium or vitamin D levels monitored.”
What are the best food sources of vitamin D?
Oily fish such as salmon, mackerel, sardines and herring are the best natural sources of vitamin D, Dr Henderson says. One portion of grilled salmon contains roughly 13mcg, while a portion of smoked mackerel has around 12mcg of vitamin D, according to the Royal Osteoporosis Society.
Egg yolk is another good source but “the amount varies by hen diet”, Dr Henderson warns. Fortified foods such as certain margarines, milks and breakfast cereals also contain vitamin D, he says. One glass of fortified soya milk contains around 1.6mcg, while a portion of fortified cornflakes contains roughly 1.4mcg.
“Diet alone often won’t supply the 10mcg-per-day target for many people, especially in winter, hence the routine supplement advice for at-risk groups,” Dr Henderson says.
Why is vitamin D3 generally recommended over vitamin D2?
The short answer is that vitamin D3 seems to be better and more effective for our bodies, Prof Llewellyn says. It’s the form of vitamin D we produce from sun exposure, and the type found in animal products such as oily fish and egg yolk.
“D3 has greater potency and longer duration of action in many trials,” Dr Henderson adds. “D2 still has a role in some fortified foods or for vegans, but D3 is usually recommended when available.”