With our moods soaring, many social gatherings ruined and countless sporting events cancelled, could the overcast, humid summers we’ve been enduring also be harming our health by robbing us of a key sun-based nutrient: Vitamin D?
With mild sunshine and rain expected for the time being after last week’s mini-heatwave, this is an important issue because vitamin D is essential for bone health, as well as keeping the immune system functioning efficiently, and is even being investigated as a way to reduce the risk of dementia.
But without access to sunlight (or the outdoors), most people seem unable to earn enough to meet their needs.
The main source of vitamin D is ultraviolet B (UVB) radiation found in sunlight, which stimulates cholesterol in the skin and initiates a series of chemical reactions that produce vitamin D.
But concerns are growing that we may not get enough sunshine, given the amount of cloudiness we’ve seen so far this summer (meaning the average sunshine hours are much lower than normal), and the weather has also been very wet (parts of the UK recorded their wettest May on record, according to the Met Office), meaning people are spending more time indoors than usual.
The weather was very wet, with parts of the UK experiencing their wettest May on record, according to the Met Office.
Even when the weather is relatively good, many of us are deficient in vitamin D. The most recent UK National Diet and Nutrition Survey found that between 2008 and 2012, almost a quarter of adults aged 19 to 64 and one in five adults aged 65 and over had insufficient levels of vitamin D in their blood.
During the dark, cloudy winter months of January to March, this figure rose to four in 10 people aged 19 to 64 and three in 10 people aged 65 and over.
Older people are at higher risk of deficiency because they are less able to absorb vitamins from food (for example, they obtain less from oily fish and eggs) and because the body produces them less efficiently.
But there’s some good news: Although we might get “a little less” sun exposure this year, this might not be a problem because there are several factors that affect how much vitamin D we make, says Adrian Martineau, professor of respiratory infections and immunology at Queen Mary, University of London.
“The ability of sunlight to synthesize vitamin D in the skin is related to the intensity of UVB radiation, which is affected by cloud cover and latitude, so the further away you are from the equator, the more atmosphere the sun’s rays have to pass through before hitting the Earth,” he explains.
So in summer, as our region tilts towards the sun, the intensity of the sun’s rays hitting the UK increases, which should help replenish Vitamin D levels.
But there are other factors that come into play, he says, including “the time of day (UVB rays are strongest between 10am and 2pm), the amount of time you spend outside, and whether or not you wear sunscreen” (although some experts say it’s rare for people to slather on sunscreen so thickly that it blocks vitamin D production).
Vitamin D is not only essential for maintaining bone health, but also for keeping your immune system functioning effectively.
And action is really important, because while you might think that vitamin D deficiency would be less of a problem in hotter countries, this isn’t the case. “In Saudi Arabia, rates of vitamin D deficiency are much higher than in the UK because it’s so hot that people are often outside in the sun,” says Prof Martineau.
Due to the fact that Vitamin D is so important to our health, in 2016 the Department of Health recommended that all adults and children consider taking a 10mcg supplement daily between October and March, as in winter we often don’t get enough sunlight to stimulate sufficient Vitamin D production.
Getting some sunlight in the spring is perhaps most important “because that’s when our vitamin D levels tend to be at their lowest and so need the biggest boost,” says Professor Martineau.
Brief periods of sun exposure can help replenish vitamin D levels, but because vitamin D is a fat-soluble vitamin, it can be stored in the body and used at a later date, but only for a limited period of time.
“The half-life of calcidiol [the form of vitamin D that circulates in the body] “Over the course of a month or two — if you’re on a submarine, or you’re suddenly deprived of sunlight — your vitamin D stores will halve every month or two,” Professor Martineau adds.
But you don’t need great summer weather to replenish your vitamin D levels: as long as you can go outside on a cloudy day, there’s still enough UVB to boost your levels, says Susan Lanham-New, a professor of human nutrition at the University of Surrey, who was part of the government working group that drew up the 2016 recommendations.
“It doesn’t necessarily matter if it’s a sunny day, as long as you’re getting enough UVB,” she told Good Health. “If it’s between April and September, the UVB wavelengths are strong enough. Even if it’s cloudy during these months, you should still get enough UVB exposure so that your body can make enough vitamin D.”
But it’s important to add that: “Our findings suggest that people should be spending at least 10 to 20 minutes in the sun a day, but never so much that they burn their skin.”
A 2018 study from the University of Manchester published in the journal Nutrients found that people with dark brown skin who don’t tan easily may need 25 minutes of sun exposure to get enough sun because their skin is less able to absorb UVB rays.
Regarding taking vitamin D supplements, Professor Lanham-New says: “For example, there is no need to take supplements between April and September unless you are too frail or elderly to go outside, or your culture doesn’t allow you to expose your skin,” adding: “There’s no harm in taking a moderate amount of supplements all year round, but it could be a waste of money.”
In fact, research has also shown that vitamin D tablets are not a complete substitute for getting the vitamin through a healthy diet.
In 2022, a five-year study from Harvard Medical School that followed 26,000 middle-aged men and women who took daily supplements reported in the New England Journal of Medicine that taking supplements did not prevent fractures or osteoporosis, even in people with low vitamin D levels.
Studies have found that supplements don’t provide the benefits you get from getting small amounts of the vitamin naturally from foods like oily fish, eggs and red meat.
Other sources include fortified breakfast cereals, breads and some children’s yogurts.
NHS nutritionist Catherine Collins adds: “Mushrooms can also be a great source of vitamin C, which is beneficial for vegans. Vitamin C is produced in the folds on the underside of the mushroom in response to sunlight, so you just need to turn the mushrooms upside down and place them on a windowsill for a few days.”
For those who need a little more courage to get outside and soak up some sunshine, there are other health benefits beyond Vitamin D.
A 2014 study conducted by Dr. Richard Weller, an emeritus dermatologist at the University of Edinburgh, found that sunlight increases nitric oxide levels.
“This chemical dilates blood vessels and lowers blood pressure,” he says. “My research shows that natural light may protect against hypertension and cardiovascular disease, two of the world’s biggest killers.”
All of this makes getting outdoors this summer even more appealing, even when it’s cloudy and humid.
Additional reporting by Lucy Elkins
Recycling starts at home
How the body “recycles” things. This week: Estrogen
Some women reach menopause later than the average age of 51. One theory for this is that women are more efficient at recycling estrogen.
When the “old” estrogen reaches the intestines after circulating through the body, it is either excreted in stool or gut bacteria, called estrobolome, produce an enzyme that “reactivates” it.
“There is some evidence that female hormones have an effect on the gut microbiome and that hormones are reabsorbed from the intestine,” says Dr Shazia Malik, consultant obstetrics and gynaecologist at the Royal Free London NHS Foundation Trust and the Portland Hospital.
