Vitamin D: How much is enough?

Henrietta Norton BSc, Dip NT, MBANT, AFMCP Co-founder of Wild Nutrition and Nutritional Therapist.

1 in 5 of us in the UK are estimated to have insufficient blood levels of Vitamin D for good health; we simply can’t produce enough of it from the sunshine alone and especially for those of us in Northern Europe. The half life of this vitamin is 3-6 weeks, so even gathered stores over the summer rapidly decline by the time we get to the deeper winter months.


Additionally, sunscreens, longer office working hours, medications such as statins and our age (those above 65years of age are 4-times lower capacity to produce it in their skin compared to younger adults) can affect our levels further. Our dietary habits have changed somewhat too and Vitamin D rich foods such as oily fish, whole-fat dairy as part of our daily diets have fallen out of favour.


For some time the Department of health have recommended an increased Vitamin D intake for ‘at risk’ groups such as the elderly (seniors have a 4 fold lower capacity to produce it from the sunshine for example), children under 5, pregnant and breastfeeding women. More recently, however the Scientific Advisory Committee of Nutrition (SACN) recommended that the UK population aged 4 years and over have an intake of 10 μg per day. This is the amount needed for 97.5% of the population to maintain a concentration of 25 nmol/L of vitamin D (25 (OH) D) in the blood when UVB sunshine exposure is minimal. For many, 25nmol/l may not even be enough to maintain optimum health, with some requiring up to 100nmol/l for optimum health.


Why do I need vitamin D?


Virtually every cell in the body has a vitamin D receptor, which, when bound to this vitamin, can influence the expression of more than 200 genes.


Previous concerns about Vitamin D deficiency have been associated with poor bone health, most notably the development of Rickets, a condition which is again on the increase according to national statistics. However the observations from the most recent large cohort studies have unraveled other key physiological roles of it and a causative relationship between vitamin D deficiency and an increased risk of cancers, pre-eclampsia, diabetes, CVD, autoimmune diseases, autism and the flu.


Should we supplement with Vitamin D?


As we’ve already established sunshine is arguably not a reliable source of vitamin D since sufficient solar radiation depends on the season and there are associated risks of skin ageing and cancer. Notably, all of Europe gets insufficient UVB intensity during the months November to the end of March, resulting in minimal skin production of vitamin D during the winter season, independent of age.


Choose wisely, opting for high quality well absorbed forms. More natural food forms provide both the active and stored forms, ready for your body to use easily. A study conducted showed that Food-Grown® vitamin D includes both the ‘stored’ (25-hydroxy) and biologically ‘active’ (1-25 hydroxy) forms of vitamin D3. The body will always need to convert any ‘stored’ form of vitamin D3 into the ‘active’ form for it to do its various jobs like supporting calcium absorption. This makes supplementing in the ‘active’ form preferential. A highly absorbable and biologically active form may also minimize the need for ‘mega dosing’.


Vitamin D rich foods


1. Seafood


Seafood is one of the best sources. If you eat fish, aim to have two or three portions per week. Choose trout, halibut, sardines, herring, salmon and mackerel.


2. Whole milk


Organic full fat milk contains much more than semi skimmed milk and is less likely to have had anything added or removed. An even better option would be unpasteurised milk from a farm shop, if you have one in your area. Unfortunately the most popular form of milk is semi-skimmed, which contains significantly lower amounts of fat soluble vitamins.


3. Chicken and duck eggs


Eggs are a great source and are so versatile and easy to make. Ensure you eat the yolk as this is where you'll find it.


4. Mushrooms


Some mushrooms have the ability to produce vitamin D when exposed to sunlight. The normal button mushrooms you find in the supermarket will contain very little of this.  Opt for a selection of portobello, maitake, morel, chanterelle and oyster mushrooms for a higher content.


Avoid foods that have been artificially fortified. Instead opt for food that contains vitamin D naturally from the list above.


Don’t be tempted to think more means more


As with many nutrients, Vitamin D follows a U-shaped curve, meaning that high levels can be just as problematic for health as low levels. An excessive intake is associated with increased risk of cardiovascular disease, kidney stones and low bone density. The latter is especially important to recognize as many will self-diagnosis with high strength Vitamin D supplements to reduce osteoporosis risk but may in fact be encouraging the ‘leaching’ of important nutrients for bone density out of the bone matrix. Look for supplements with your recommended daily allowance and better absorption instead.


To understand your individual need, consider getting the guidance of a well trained nutritional therapist or functional medicine practitioner or requesting a Vitamin D blood test with your GP.


For more on the importance of vitamin D and supporting your health for this season, see 'To D or not to D?' and 'Autumnal equinox: 9 Tips to support your health this season'

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