Nutrition Seasonal UV-level variations make it almost impossible for many of us to maintain a healthy vitamin D status without supplements.
Seasonal UV-level variations make it almost impossible for many of us to maintain a healthy vitamin D status without supplements.
Latitude, sunscreen use, outdoor activity, clothing and skin pigmentation can also affect levels.
Question:
At 58, I was diagnosed with pre-osteoporosis and prescribed monthly 50,000IU vitamin D3 tablets, among other things. Getting a new script from the GP every three months involves much faffing around. Could I take a supermarket vitamin D3 supplement of 1000IU daily instead, with extras, to get the same monthly dose? And would the quality be the same?
Answer:
About 5% of adults in this country are vitamin D deficient, as are significant numbers off children – indeed, one study found 24% of breastfed infants aged six months or under were deficient in vitamin D. Given the essential role this vitamin plays in our health, we must maintain optimum levels throughout our lives, but in New Zealand that is easier said than done. Vitamin D has long been known for its essential role in bone metabolism and muscle function, with low levels linked to rickets in children and osteoporosis and osteomalacia ( bone softening) in adults. More M recently, accumulating evidence e has linked vitamin D status to the severity and frequency f of respiratory infections in children and adverse pregnancy outcomes. Observational studies h have also highlighted potential relationships between vitamin D status and colon cancer, multiple sclerosis and diabetes mellitus.
There are three primary sources of vitamin D: skin exposure to ultraviolet B (UVB) from sunlight, dietary supplements and a small range of foods, such as oily fish, milk, milk products, eggs and liver. Some
margarines, spreads, dairy substitutes and liquid meal replacements also have added vitamin D.
However, food sources do not meet our requirements, which means most people are dependent on their skin producing vitamin D when it’s exposed to sunlight. However, we must balance the risk of skin damage and skin cancer from sun exposure with the potential for a vitamin D deficiency. Moreover, latitude (the distance from the equator), sunscreen use, outdoor activity, clothing and skin pigmentation can also affect vitamin D levels.
Finally, for many New Zealanders, seasonal UV-level variations make it almost impossible to consistently maintain a healthy vitamin D status. In Auckland, for example, UV levels vary tenfold between summer and winter.
The Ministry of Health recommends at-risk groups take a single 50,000IU vitamin D supplement monthly. These groups include people who avoid sun exposure, are housebound, have low mobility or have naturally dark skin. In addition, those who live in the cooler southern regions and spend little time outdoors in the middle of the day may also be at risk of a deficiency and could consider supplementation during the cooler seasons. Those with liver or kidney disease are also vulnerable.
One study found 24% of breastfed infants aged six months or under were deficient in vitamin D.
However, Associate Professor Pamela von Hurst, co-director of Massey University’s Vitamin D Research Centre, says a daily supplement may be a better option than a monthly one.
“There is emerging evidence that daily doses are more effective than the monthly dose, especially for conditions related to immune function, not so much for bone, but it could be the case there as well,” she says.
Indeed, a New Zealand review of vitamin D supplementation, published in the British Medical Journal, found daily or weekly vitamin D supplements were more beneficial than monthly or less-frequent supplements in preventing acute respiratory-tract infections.
Von Hurst recommends taking 2000IU a day over winter, perhaps reducing to 1000IU over summer (unless your sun exposure is limited throughout summer). Most well-known brands are adequate in terms of quality, she says.
For the rest of us, vitamin D status can be lifted during winter – without the risk of sunburn – by exposing our arms, face and neck during the middle of the day. About 30 minutes or more is ideal. Von Hurst says, “Go for a nice brisk walk that warms you up, then you’re more inclined to bare a bit of skin.” l