Why do I need vitamin D?
The reason most of us associate vitamin D with teeth and bones is because, more than 100 years ago, it was discovered that a deficiency in this vitamin could cause children to develop rickets, a condition that causes soft, weak, and deformed bones. like a bent leg.
“Vitamin D helps the body absorb calcium and phosphorus from the gut,” explains Dr Milli Raizada, a general practitioner and senior clinical lecturer in primary care at the University of Lancaster School of Medicine.
“That calcium, in turn, mineralizes the bones and strengthens them.” For a long time, this was thought to be the only benefit of vitamin D. However, as Prof Martin Hewison, director of the Institute for Metabolism and Systems Research at the University of Birmingham explains, in recent decades, science has moved forward. .
“About 25 years ago, people discovered that vitamin D receptors – the molecules that transmit the effects of vitamin D – are present in more tissues than just the gut. It’s in cancer cells, in muscles, in the immune system — all places unrelated to rickets prevention.
So people are starting to look at other roles it might play and some research has shown that it seems to slow cancer cell growth, can regulate immune system cells, can act as an anti-inflammatory agent and enhance antibacterial and antiviral effects in the immune system. cell.”
But most of these functions have been observed in animals or cell cultures, which is why there is still no conclusive evidence that the same is true in humans.
“A number of studies have shown that people with autoimmune diseases, such as type 1 diabetes, rheumatoid arthritis and multiple sclerosis are more likely to be deficient in vitamin D. And there are other diseases, such as Parkinson’s and Alzheimer’s where patients generally have lower levels of vitamin D than the population who Healthy.”
But, Prof Hewison warns, this study shows an association, not necessarily a causal one. “The only way to know if higher levels of vitamin D will prevent disease is to supplement people with vitamin D over a very long period of time and that is very difficult, and expensive to do.” Hence the controversy over the actual benefits of vitamin D.
What is a vitamin D deficiency?
Vitamin D deficiency in children can cause crooked legs and rickets, but in adults it is more likely to manifest itself as general fatigue, bone pain, and muscle aches. And, as Dr Raizada points out, it can also make older people more prone to falls.
A blood test done by your GP can determine your vitamin D levels, but according to Nice’s guidelines, you’re unlikely to be tested unless you show symptoms associated with a deficiency, as described above — even if you’re in one of the risk groups.
“People at risk for vitamin D deficiency include children, those over 65 years of age, women who are pregnant or breastfeeding, and anyone who has problems absorbing the vitamin, or problems with the kidneys or liver, which help metabolize vitamin D. said Dr Raizada.
“Because most of the vitamin D in the body is synthesized by the body through exposure to sunlight on the skin [see below]dark-skinned people, who have more melanin in their skin, may also be deficient.”
However, what constitutes a deficiency varies around the world. Here in the UK, vitamin D levels are measured by looking at the number of nano moles (nmol – a very small unit of measurement of weight) in a liter of blood – less than 25, and you are considered less, 25-50 is not enough and more than 50 is enough Enough.
Prof Hewison believes the UK should be more aspirational about vitamin D levels in the population. “In North America, they say you should aim for 50nmol/l and above,” he said.
“But there they add it to milk, and orange juice. Here in the UK, not only do we not do that, but when the Science Advisory Committee on Nutrition set out their advice in 2016, they advocated not going below 25nmol/l, which seems a very timid approach. Their argument is that the only proven link is between vitamin D deficiency and rickets, so if you get people over the threshold for that, that’s acceptable. However, there is a lot of data, including mortality data showing that mortality is much higher when levels are below 50nmol/l, which is why I and many of my colleagues in the UK think we should aim to be above 50nmol/l, not just below 25nmol /l.”
What are good sources of vitamin D?
While diet can be a good source of vitamin D – you see oily fish like herring, mackerel and salmon, as well as egg yolks – it’s not a very good source, and even here in the UK, where there isn’t much sunlight. , we still get 90 percent of vitamin D from exposure to sunlight.
“Our skin naturally contains vitamin D precursors,” explains Dr Raizada. “When the UVB rays in sunlight hit the skin, they start the process of converting these vitamin D precursors into a form the body can use. Further changes occur first in the liver and then the kidneys, until an activated form of vitamin D is produced.
According to consultant dermatologist Dr Anastasia Therianou, someone with Caucasian skin needs about nine minutes of sunlight between noon and 3pm.
Those with darker skin, closer to 25 minutes. These figures are based on not wearing sun protection and 35 percent of exposed skin area — about what you’d show off if you wore shorts or a simple skirt with a T-shirt.
A little daily sun exposure is better than going out once a week without sun cream for an hour because it balances your vitamin D needs with your UV-related risk of skin cancer.
However, Dr Therianou points out that if a person has a sun-sensitive condition, such as lupus or skin cancer, it’s best to get vitamin D from a supplement.
This was echoed in a 2021 paper titled Vitamin D and Skin Cancer: An Epidemiological, Patient-Centered Update and Review published in the journal Nutrients.
The authors concluded that: “Sun protection recommendations among people at risk for skin cancer or patients with a personal history of skin cancer should be maintained, and… neither natural nor artificial sun exposure should be encouraged as a primary source of vitamin D. Given that the vitamin D diet and additionally are functionally identical to those produced after UV exposure (and also more reliable and scalable), it should be the preferred source of this vitamin.
Of course here in England we don’t have much choice in this regard. In fact, due to the country’s lack of sunlight, the NHS recommends between September and March adults take a daily supplement of 10mcg (micrograms), or 400IU (international units).
Research shows that this will be enough to ensure that 97.5 percent of the population has levels equal to, or greater than, 25nmol/l.
And those at risk of deficiency — people with darker skin, adults who stay at home, or people who cover up a lot when outside — should continue to drink it year-round. Another group at risk for deficiency includes patients taking drugs like orlistat (aka semaglutide or Ozempic) that stop fat absorption. And people with high BMI. “It’s very common for people with a high proportion of adipose tissue, or fat, to have lower levels of circulating vitamin D,” said Prof Hewison.
“Vitamin D is stored in adipose tissue which means it is stored in a way that it cannot be used. There are currently several studies being conducted at the University of Bath to see if exercise can help move vitamin D from adipose stores into circulation.”
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