Food supplements: Should we all be taking vitamin D?
Half of us in the UK take vitamin supplements on a regular basis. Now that winter is upon us, should we all be supplementing our diet?
Vitamins and food supplements are big business in the UK, with the market valued at £414 million in 2015. A 2018 survey by the Food Standards Agency found that 48 per cent of adults in the UK reported they were currently taking supplements on a regular basis, and in the US, the number is as high as 77 per cent.
So, are all these supplements making us much healthier? A review from 2018 found no conclusive evidence that taking multivitamins or supplements reduced the risk of mortality from cardiovascular disease or cancer, and some, such as vitamin B3 and antioxidants, could even increase the risk.
Reporting on this study, the Guardian described most vitamin and mineral supplements as ‘a waste of money’. Taking vitamin D had no noticeable effect on mortality at all, and yet the NHS recommends that everyone in the UK should consider taking vitamin D supplements throughout the winter, regardless of age, health and sex.
What does vitamin D do?
The group of molecules collectively known as vitamin D serve several purposes in the body, most importantly regulating levels of calcium in the blood and how much the body absorbs from food. In the summer, the body produces most of the vitamin D it needs using the energy from UV light hitting the skin, with smaller amounts absorbed from foods such as red meat, oily fish and egg yolks.
However, in the winter months, many people see very little sunlight and levels of vitamin D can drop significantly. By the end of the winter, up to 40 per cent of adults in the UK are deficient, particularly those with darker skin.
Deficiency in vitamin D causes a condition which is called osteomalacia (literally meaning ‘bone softness’) when it affects adults, or rickets in children, in which the bones gradually soften as calcium leaks out.
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“That can cause muscle pain and joint pain,” explains Dr Gail Rees, Senior Lecturer in Human Nutrition at the University of Plymouth. “They could easily fracture and suchlike.” So, while vitamin D supplements won’t have much impact on the length of your life, they could improve your quality of life by protecting you from aches and pains.
Taking supplements isn’t without risk. Extremely high levels of vitamin D in the body, in combination with high levels of calcium, can result in a condition known as hypercalcaemia, where calcium starts to build up in the blood.
Some vitamins, like vitamin C, are water-soluble, meaning the body can only absorb so much and any excess is flushed out of the body in urine. Vitamin D, however, is fat-soluble, so it can’t be expelled when the body has too much.
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However, the risk of hypercalcaemia is low, Rees says, as long as you follow the instructions correctly. “I would say it’s unlikely if you’re taking at the recommended levels,” she says. “So, on the packet, it should say an RDA, or a recommended daily amount. I wouldn’t take a supplement that goes over that amount.”
Why take supplements?
While it’s true that supplements may won’t help you live longer, most people tend to take vitamins and minerals for the more nebulous wellbeing effects they offer, such as extra vitality, more energy and a strengthened immune system.
“If you are deficient in iron and are suffering from anaemia, then taking an iron supplement certainly will give you more energy, as iron is involved in carrying oxygen in the red blood cells,” explains Rees.
So, in that sense, taking supplements can stop you from feeling lethargic, a common side-effect of iron deficiency. But vitamins can’t give you energy directly: their purpose is to help the body process the energy from carbohydrates, fats and proteins.
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Vitamins can’t prevent you from catching winter illnesses either. “If you have enough vitamins and minerals from your diet, there is no evidence that taking more will prevent you catching an infectious disease,” says Rees. However, if you’ve already got a cold, taking vitamin C and zinc supplements could do you good: both have been shown to reduce the duration of colds.
Unfortunately, you can’t use food supplements to make up for an unhealthy diet either. “You could replace the vitamins and minerals that you’re missing in your diet by taking a supplement,” says Rees. “So, that would stop you becoming deficient in any of those vitamins or minerals, but there’s no evidence that doing that would reduce your risk of chronic disease.”
The main problem with a diet full of processed foods and low on vegetables isn’t the vitamins and minerals as such, but the lack of disease-preventing compounds found in plant foods and the high levels of the nutrients known to cause disease: salt, sugar and fat.
So, should we be taking vitamin D over the winter? Rees says there are three key nutrients we should consider supplementing, regardless of whether we have been diagnosed with a deficiency.
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Firstly, anyone who expects they might become pregnant should take 400 micrograms of folic acid. “Even women who are not pregnant, or not specifically trying for a baby, it may be useful for them to have the recommended amount of folic acid for pre-conception, just in case they did become pregnant,” she says.
Those following a vegan diet should also consider taking vitamin B12. “It’s only really available in animal foods, so meat, chicken, fish and dairy foods, apart from foods that have it fortified.”
Finally, Rees says yes, she would recommend everyone to consider taking vitamin D through the winter. “We’re not saying that people are necessarily going to get rickets or deficiency diseases, but we do know that during winter, vitamin D levels drop really low.”