Vitamin D is both a nutrient and a hormone. It was thought that we made enough vitamin D through the action of the sunlight on our skin and so it was often referred to as the “sunshine vitamin”. Natural foods containing vitamin D were not relied on so much to meet our needs.
It now seems clear that a large percentage of Irish people and immigrants living in this country can’t rely on this sunshine factor to produce sufficient vitamin D. Because of our northerly latitude, we are exposed to an inadequate type and amount of UV sunlight in this country.
Darker skinned people need 10-50 times the amount of exposure to meet their needs at this latitude. Particularly at risk are those who are confined indoors due to work or illness; those who have limited sunlight exposure for religious or cultural reasons; and those who protect their Celtic skin with total UV blocks to reduce their risk of melanoma.
Deficiencies are also more likely in conditions causing fat mal-absorption such as inflammatory bowel disease or after gastric bypass surgery.
Over 20 cases of the bone-softening disorder rickets were recorded at two Dublin hospitals in infants and toddlers during a five-year period, according to the Food Safety Authority of Ireland. A subsequent report recommended the implementation of a national policy of vitamin D supplementation (5µg) in all infants aged 0-12 months in Ireland.
The recommended intake of vitamin D for adults is 0-10µg, but the RDA on food labels is listed as 5µg, as the assumption is that we get some vitamin D from the sun.
However, when you look at the nationally representative surveys, a substantial proportion of 18-64 year olds have low vitamin D intakes, with 72 per cent of men and 78 per cent of women having average daily vitamin D intakes of less than 5µg, and over 90 per cent having daily intakes of less than 10µg, according to a 2011 study of Irish people. In this study, the mean daily intake among 18-64 year olds was found to be just 4.2µg.
Vitamin D contributes to the normal absorption and utilisation of calcium. We absorb as little as 15 per cent of the calcium we consume, when we are vitamin D deficient. Bone is a living tissue and over time insufficient calcium can weaken the existing bone and prevent the formation of new bone, potentially resulting in osteoporosis.
Recent research has also looked at vitamin D’s role in a variety of diseases other than bone health. Mostly through epidemiological evidence, studies have highlighted an association between low vitamin D status and an increased risk of cardiovascular disease, diabetes, certain types of cancer, cognitive decline, depression and autoimmune diseases.
In the Health Professional Follow-Up Study, Prof Edward Giovannucci, of Harvard School of Public Health, found that men who were deficient in vitamin D were twice as likely to have a heart attack as men who had adequate levels of vitamin D.
There are, however, many unanswered questions. More research is needed before we can recommend supplementation for risk reduction.
Dietary sources of vitamin D
The problem with vitamin D is that it’s not widely found in many natural food sources. The best natural source is an oily fish such as salmon, tuna, mackerel, herring and sardines. Eggs also contain a little vitamin D. Most of us rely on daily fortified foods to boost intakes, as oily fish might be eaten once or twice weekly and perhaps not at all. An increasing number of foods are being fortified, for example, various milks and yoghurts, certain orange juices, even breakfast cereals.
Boosting dietary vitamin D intake *
Try a fishy Friday dish using salmon, trout, mackerel, herrings, sardines and fresh tuna.
Choose tinned oily fish as a lunch option.
Choose a fortified milk and breakfast cereal.
Include up to seven eggs in a week, if your cholesterol is normal.
Consider a supplement if you can’t meet your intake through diet alone.
Note*: Pregnant and nursing women should avoid unpasteurised eggs and dairy foods, avoid soft and blue cheeses and limit their consumption of seafood that may contain dioxins and mercury. Discuss the full list of foods to avoid or include with your GP, practice nurse or dietitian.
Salmon and courgette tray bake
Serves 4
4 fillets of salmon
2 courgettes cut diagonally into 1cm thick slices, no thicker
1 packet cherry tomatoes on the vine, cut in half
12 baby potatoes
6 tbsp olive oil
1 tbsp balsamic vinegar
2 sprigs of fresh rosemary
Salt and pepper
Boil the baby potatoes until fully cooked, drain and cut in half. Preheat the oven to 180°C. Drizzle a little of the olive oil onto a roasting tray and season the tray. Place the salmon, skin side up, and scatter the potatoes, courgettes and tomatoes around, followed by the rosemary, then season. Drizzle with the remaining olive oil and balsamic vinegar over.Place into the oven for 12 minutes.
Remove the salmon to warm plates, remove the rosemary and throw away, swirl around the remaining ingredients in the tray to coat in the juices and then serve with the salmon.
Thai-inspired tuna stir-fry
Fresh tuna is marinated, stir-fried and tossed with tomatoes, red chilli, basil and fresh coriander. Serve with steamed jasmine rice. Ready in 35 minutes.
Serves 4
2 tbsp fish sauce
4 tbsp fresh lime juice
1 tbsp honey
0.5kg (1lb) fresh tuna steaks, cubed
2 tbsp olive oil
4 fresh tomatoes, chopped
1 bunch spring onion, finely chopped
½ small fresh red chilli, seeded and chopped
Handful fresh chopped coriander
Handful fresh chopped basil
In a small bowl, mix together fish sauce, lime juice and honey. Place tuna in a large, plastic, sealable bag, and pour fish sauce mixture over the tuna. Shake to combine. Refrigerate for 1 hour.
Heat ½ tbsp olive oil in a wok over a high heat. When the oil is very hot, almost smoking, place half the tuna in the pan; cook and stir for 1 minute, or until desired doneness. Transfer cooked fish to a large bowl. Repeat with remaining oil and tuna.
Toss warm fish with tomatoes, spring onion, red chilli, coriander and basil. Serve.
Paula Mee is lead dietitian at Medfit Proactive Healthcare and a member of the Irish Nutrition and Dietetic Institute.
medfit.ie
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