Vitamin D is now commonly thought by scientists to be crucial to so many aspects of our physical, mental and emotional health and wellbeing. It supports our immune function and helps to reduce inflammation, but it is also one of the most likely vitamins for us to be deficient in.
The two most common compounds of this crucial vitamin are D2, which we get from food, and D3, which we get from sunlight, (specifically UVB radiation when the index is 3 and above) which causes a chemical reaction in the lower levels of our skin. Production can be halted by sunscreen products, but also sunburn, so a real balancing act is needed here. People with darker skin complexions can also have poorer production. D3 is the more powerful of the compounds and can raise blood levels by almost twice as much as D2.
Food sources are oily fish, liver, egg yolks, cheese and mushrooms that are grown outdoors or under UV light, meaning that vegetarians and vegans can only get D2 from these mushrooms or fortified plant based milks. This, along with our not always so sunny climate, goes a long way to explain why so many of us are deficient.
For many people, symptoms of deficiency can be very subtle, but may include: low immunity, slow wound healing, hair loss, bone pain and muscle weakness, cognitive impairment in old age and depression.
Whether eaten, or absorbed by the skin, vitamin D is transported to the liver and kidneys where it is converted into an active hormone form. As a hormone it assists with the absorption of calcium, magnesium, and phosphate, all of which help healthy bone growth and maintenance. This hormone also helps to release neurotransmitters such as serotonin and dopamine, helping with brain function and development. A study at Trinity College Dublin has shown that low levels in older adults increased the risk of depression by up to 75%. An international study funded by the UK National Institute for Health Research, which followed 1600 people for an average of 5.6 years, showed that those deficient in Vit D had a 69% higher risk of developing dementia, while those who were severely deficient increased their risk by 122%.
Recent research is also showing the role vitamin D plays in the prevention and treatment of type 2 diabetes and high blood pressure. Vit D has also been linked to eye health, especially conditions categorised by inflammation such as age related macular degeneration and dry eye syndrome. Research has shown that women under the age of 75 with a higher D intake were nearly 60% more likely to develop AMD compared to those with a low intake. In another study scientists found that 52% of women with low levels experienced dry eyes, compared with just 4% of those with higher levels.
The NHS guidelines on supplementation is 400iu daily. But many experts will recommend up to 1000iu daily. For those at risk of deficiency this is considered a very safe daily dose. Do please make sure that your supplements are a good quality, and do not exceed the safe dose without proper medical advice.