Should You Supplement with Vitamin D This Winter?
Table of contents
What is Vitamin D?
Vitamin D is sometimes referred to as the “sunshine vitamin” because, although we get a small amount from foods we eat, we obtain the vast majority from the sun. Our skin absorbs UVB radiation in sunlight and converts this to a precursor of vitamin D, which is then metabolised in the kidneys and liver into the active form of the vitamin1.
The Northern Latitude Problem
The vast majority of UVB radiation never reaches the earth, as 99% is absorbed by the atmosphere1. In winter months in the Northern hemisphere, the amount that reaches us is diminished even further because the angle of the sun to the earth means light has further to travel. Unfortunately for those of us living in the most northern latitudes, including the UK and the northern parts of Europe, we are unable to obtain any vitamin D at all from the sun between October and March, even on a sunny day2.
Vitamin D and Bone Health
It’s commonly known that vitamin D is important to bone health because it helps with the absorption of calcium. When the industrial revolution blocked out sun through smog filled skies, rickets became prevalent in children, until vitamin D fortified foods corrected the issue1.
Thankfully rickets is no longer a common concern in the Western world, but low levels of vitamin D continue to have an impact on our bone health. Without vitamin D, very little calcium can be absorbed by the bones and studies have found a direct link between low levels of the vitamin with low bone density, leading to an increased risk of hip fracture, osteoporosis, osteopenia, osteomalacia, and muscle weakness3. We also become less able to make vitamin D from sunlight as we age1, exacerbating the issue. Studies found anywhere between 40 to 100% of older adults in the USA and Europe were deficient in Vitamin D3, and one study found 93% of patients admitted to hospital for bone pain were vitamin D deficient4.
Vitamin D and the Immune System
You may have heard that vitamin D can support the immune system. A Japanese study found that school children given vitamin D supplements during winter were less likely to get flu and had a reduced number of asthma attacks5. And recent research has suggested that vitamin D supplementation may decrease the risk of becoming more seriously ill from Covid 6,7,8.
The prevalence of autoimmune diseases like MS, Crohn’s disease, rheumatoid arthritis, and type 1 diabetes are higher in parts of the world that have less sunlight, and it’s thought that this is due to vitamin D’s role in the immune system 9,10,11. Finland, which has just two hours of sun in winter in its Northern parts, has the highest rate of type 1 diabetes in the word10, while the Northern regions of Scotland have been found to have particularly high levels of MS11.
Vitamin D and Other Areas of Health
In fact, vitamin D receptors have been found in virtually every cell and organ of the human body, highlighting its importance in numerous body functions1.
Just some of vitamin D’s functions include:
- Cardio-protective12: reducing the risk of hypertension13, coronary artery disease13, and the increased susceptibility of cardiovascular disease 12,13.
- Cancer protective: numerous studies have found a correlation with a lack of vitamin D from the sun and an increased risk of a wide range of cancers14.
- Insulin resistance and sensitivity: vitamin D has been found to protect against type 2 diabetes15.
- Brain health: low levels have been associated with cognitive decline16, dementia17 and Alzheimer’s disease17,18.
- Mental health: low levels have been associated with depression19 and schizophrenia20.
How Much Vitamin D Do We Need?
The RDA (recommended dietary allowance) of Vitamin D in the UK is 400 IU21. However, this is a minimal amount, set to prevent rickets and most nutrition experts agree much more is required to optimise health. An article published by the Royal College of Physicians called for an urgent review of Vitamin D RDA in the light of the COVID-19 pandemic, urging recommendations to go up to at least 800 IU per day7.
Dr Holick (author of The Vitamin D Solution) first identified the active form of vitamin D3 and has written extensively on the topic. These are his recommendations for daily vitamin D intakes2, much greater than the official recommendations.
- 0-1 year olds: 400-1,000 IU
- 1-12 year olds: 1,000 - 2,000 IU
- 13 year olds + : 1,500- 2,000 IU
- Lactating women: 4,000 - 6,000 IU
Can I Take Too Much Vitamin D?
Over the years there have been concerns about toxicity from vitamin D supplementation as excessive amounts can lead to hypercalcemia: excessive calcium in the blood, which can lead to heart and brain defects1. However, it’s now thought that these concerns have been inflated: you would need to take very extreme doses for several months before being at risk of toxicity1. Holick advises that the safe upper limit for adults is 10,000 IU/day (2,000 for babies under 1 and 5,000 for children between 1-12 years)2, much more than most people would commonly take. Vitamin D synthesised from the sun can never cause toxicity1.
Do I Really Need A Supplement?
Vitamin D can be stored in fat tissue22, so in theory if you obtain high levels during the summer months, then this could keep you going through the winter. However, very few of us spend as much time outdoors as our ancestors would have. We work, socialise, travel, and even exercise indoors. When we do spend time in the sun, we use sunscreen which blocks the beneficial production of vitamin D as well as the sun’s more harmful effects. In summer months, 5 to 30 minutes of unprotected sun exposure to your face, arms and hands at least three times a week is considered sufficient to keep your blood vitamin D levels out of deficiency.23
Those living in the far North have also traditionally kept their levels of vitamin D adequate through diet, by eating high quantities of blubber and liver of seals and whales1: not foods on the menu for most of us! Some foods like liver, egg yolks, oily fish, and shiitake mushrooms do contain vitamin D, but you would have to eat a large amount to reach adequate requirements. For example, 100 grams of high-quality wild salmon contains 1,000 IU of vitamin D. But farmed salmon contains only around 250 IU per 100 grams, a bowl of fortified breakfast cereal may contain 100 IU, and an egg yolk just 20 IU2.
It’s thought that a billion people around the world are deficient in Vitamin D3 and those of us living in Northern latitudes during the winter are at greater risk of being one of them. If you spend a lot of time outside in summer, with uncovered arms and legs and no sunscreen, your levels may be adequate2, but the rest of us should seriously consider a supplement.
In 2016, a governing body – Scientific Advisory Committee on Nutrition (SACN) published a report on Vitamin D and its health outcomes. SACN concluded that all adults should be taking 10ug (400 IU) of Vitamin D daily in Winter months (October-March). With that said, they highlighted some of us may need more than 400IU.
Who may need more than 400IU?
- Infants and young children up to 5 years of age
- Pregnant and breastfeeding women
- Anyone over the age of of 65 (especially women due to risk of osteoporosis)
- Those who have no or limited exposure to the sun (including people who cover their skin for cultural reasons)
- People who have darker skin
What Sort Of Supplement Should I Take?
Vitamin D can be supplemented in two forms: D2 or D3. Read more about the two forms on our blog, here. Vitamin D3, which is the active form and more useful as a supplement, is often made from lanolin, which makes it unsuitable for vegans. However, at Feel, we only use D3 derived from lichen- a vegan source. You can find that in good levels in several of our products: our Multivitamin for all-round health, Feel Joints, for bone health, Feel Immunity, and Feel Pregnancy.
2Holick, M.F., 2010, The Vitamin D Solution, Plume, USA