Comment augmenter vos niveaux de vitamine D cet hiver

It's that time of year where we once again swap our sunny summer activities for crisp autumnal walks and dark, cosy evenings in. While there may be many aspects of autumn we enjoy, one thing we do not get to do is enjoy much sunshine. So what happens to our levels of vitamin D - the so-called 'sunshine vitamin' - over autumn and winter?

Vitamin D and sunlight

Sian Porter, dietitian and spokesperson for the British Dietetic Association (BDA) says: "Vitamin D is known as the sunshine vitamin because sunlight on skin outdoors produces vitamin D. Everyone should try to spend some time outside daily in the sun whilst being sun-safe and avoiding burning.

"Even though we call it a vitamin, vitamin D is different because it is actually a hormone - which is a chemical messenger. Unlike some other vitamins, we can make it in our body through the action of sunlight."

The relationship between vitamin D production and sunlight is a straightforward case of the stronger the sunlight, the more vitamin D our bodies make. The amount of sunlight we get in the UK summertime enables most of us to produce healthy levels without having to think about it. Which is great, as vitamin D is integral to our health.

Vitamin D and winter

In the winter months we do need to think about our vitamin D production. From October to March, the ultraviolet light from the sun is not strong enough during the shorter, darker days to produce sufficient vitamin D levels.

Instead, unless we're taking supplements, we get nearly all our vitamin D from the food we eat. The problem is that even when we eat the right foods, those foods are unlikely to contain enough vitamin D to make up for the lost sunlight.

Official guidance now encourages us to take action in order to protect ourselves from vitamin D deficiency and associated health hazards. According to healthcare experts, this is a job we are all tasked with regardless of age, ethnicity, location and lifestyle.

The risks of vitamin D deficiency

The geographical location of the UK and lack of strong sunlight for half the year means that everyone should be conscious about their vitamin D intake in winter. However, there are several factors that contribute to higher chances of low vitamin D levels and carence en vitamine D.

Babies and children

Babies are vulnerable to deficiency, because some are born with low levels of vitamin D and some are unable to get enough through breast milk. Vitamin D deficiency can damage bone development in growing babies and children because it affects calcium levels.

They can develop rickets, which is a condition that includes stunted bone growth, bone deformities, fractures, fits and pain. Many studies have linked vitamin D insufficiency and deficiency with bone and limb problems in children.

Adults and the elderly

In adults, vitamin D deficiency can cause tiredness and general aches and pains of various degrees of severity in the ribs, lower back, hips, pelvis, thighs, shin bones and feet. Hairline fractures - a small crack or bruise on the bone - can happen.

In more severe cases, poor vitamin D levels can result in osteomalacia - a condition in which bones become soft, weak and prone to breakage. Without sufficient vitamin D, the minerals that are needed to make bones strong are unable to enter, resulting in weak muscles and bone pain.

Ostéoporose affects older people the most. Age UK warns of the dangers of poor vitamin D levels in the over-50s. It is thought that more than 1 in 2 women and 1 in 9 men in this age group will break a bone due to osteoporosis. PHE and NICE also warn that there's a higher likelihood of falls in older people, which can result in serious injury.

What makes someone more at risk?

There are a few factors that increase your chance of vitamin D deficiency.

The relationship between people with dark skin living in northern climates where the sun is weaker - such as the UK - and low vitamin D levels has been confirmed in many studies. In one study of around 450,000 people aged 40-69 years, 53% of Asian and 35% of Black people had vitamin D deficiency, compared to 12% of white people.

PHE and NICE also say that people with dark skin have a higher likelihood of vitamin D deficiency, and recommend anyone with African, African-Caribbean or south Asian backgrounds continue to take vitamin D supplements over spring and summer

Porter goes on to list other factors that can contribute to lower vitamin D levels.

How to boost your vitamin D intake

Although you may have little control over some of these factors, it's important to understand the ones you can change. The key to boosting your vitamin D levels when it's most needed over the winter months is a combination of healthy lifestyle habits, such as supplementing the right foods with vitamin D tablets.

Food for thought

Porter explains that there are a few foods that contain vitamin D.

"The best source is oily fish - such as salmon, sardines and mackerel," she says. "Other sources include egg yolks, red meat, certain mushrooms, and fortified products such as spreads, yoghurts and breakfast cereal."

"It is difficult to get enough vitamin D from food alone," adds Porter. "But including these food sources in your diet will help."

The BDA makes it clear that sunshine - not food - is where you get most of your vitamin D. Even a régime alimentaire sain that includes the food listed above is unlikely to provide sufficient levels.

One-a-day supplements

Compléments de vitamine D can make all the difference - so long as you combine them with a healthy, balanced diet and time outdoors.

According to official guidance on the PHE website, you - including all pregnant and breast feeding women - should take a daily supplement of 10 micrograms (400 international units - IU) during autumn and winter. Babies under 1 year need slightly less - between 8.5 and 10 micrograms - unless they have over 500 millilitres of fortified formula milk daily.

If you have darker skin tones, a vitamin D supplement of 10 micrograms should be taken all year around as you may not be able to make enough vitamin D from sunlight.

As always, too much of anything can be dangerous, and it is possible to take too much. However, up to 100 micrograms (4000 IU) a day is considered acceptable.

BDA also cautions against taking more than one multivitamin a day, as too much vitamin A can cause bone and liver problems.

Vitamin D supplements and multivitamins are widely available to purchase from supermarkets, health food shops, and pharmacies. They can come in many forms such as flavoured chewable sweets, making them more appealing to children. Pregnant or breastfeeding women - as well as children aged 6 months to 4 years - may qualify for 'Healthy Start' vitamins containing vitamin D.