By Shelly Meltzer & Associates, Dietary Practice at SSISA
Why is it important?
The role that Vitamin D has in health, training and performance is well documented. Besides its important role in bone health, muscle strength and immune function, some evidence suggests that vitamin D may also help reduce the risk of developing chronic diseases and auto-immune disorders, as well as certain types of cancer.
With winter approaching it is especially important to consider your Vitamin D intake:
For most human beings, the major source of vitamin D is from exposure to the sun. Factors including the time of day, season, amount of cloud cover, smog, latitude, sunscreen use and skin pigmentation, will influence this. For those of us living in Cape Town, the amount of Vitamin D3 that is synthesized in the skin in response to ultraviolet B rays may be less between June and August, because of increased cloud cover during these months.
People who spend most of their working hours inside, and athletes who do most of their training indoors may also experience reduced sun exposure.
What about food sources of Vitamin D?
Vitamin D3 (cholecalciferol) is mostly found in animal-sourced foods, and some fortified foods. Oily fish (sardines, herring, mackerel, tuna, salmon, snoek), cod liver oil, egg yolks, red meat, and fortified dairy, margarines and cereal products are the main food sources. Wild caught fish will have more Vit D than farmed fish, depending when it is caught and the time of year. Some studies have shown that vitamin D levels in Wild caught salmon can be as high as 900IU (22.5mcg)/ 100g whereas farmed salmon will only have 240IU (6mcg) per 100g. The recommendation is to consume at least 300g of fatty fish per week to try to meet vitamin D requirements.
Eggs can also have varying vitamin D contents depending on where they are raised. Free range chickens spending time in the sun produce eggs with higher vitamin D levels (572IU (14.3mcg)/100g) than chickens that are kept indoors (152IU (3.8mcg)/ 100g).
There is very little Vitamin D in vegetables, fruit and grains. Wild mushrooms or mushrooms treated with UV light are an exception. When exposed to UV light they can synthesize vitamin D2 (ergocalciferol), however Vitamin D3 is more effective than vitamin D2 at raising vitamin D blood levels.
In certain countries cow’s milk may be fortified with vitamin D, however in South Africa this is not standard practice because of the assumption that we receive sufficient sunlight. Some plant-based milks may be fortified, but amounts vary and very few brands in South Africa fortify their plant milks with Vitamin D.
How much is needed?
This depends on a person’s stage of life. For adults between 19-70 years, the RDA is 600 IU (15mcg) and for adults older than 71, it is 800 IU/day (20 mcg) per day.
What about supplements?
People who may be at risk of not getting enough vitamin D include: pregnant and breastfeeding women, babies and young children under 5 years, people aged 65 and older, people with limited sun exposure, people with darker skins; vegans and vegetarians, smokers, and people who are post gastric bypass (due to malabsorption).
It is important to be aware that Vitamin D has the potential to be toxic, so before reaching for a supplement, people should know their blood levels as well as their risk factors. Vitamin D supplements can also react negatively with certain medications (for example, it can decrease the efficacy of the medication), so it is always best to check with a doctor or registered dietitian first before supplementing.
A ’food first’ approach (foods provide an array of nutrients) and focusing on optimizing intake of food sources of vitamin D (as well as sun exposure where possible) is recommended as the first step to take. Vegetarians/vegans, older people, those with higher needs as indicated above, or those with malabsorption may need to consider supplementation.
IF YOU ARE INTERESTED IN HAVING YOUR DIET ASSESSED AND GETTING FURTHER ADVICE, YOU SHOULD CONTACT A REGISTERED DIETITIAN.