- through foods (although very few foods are good, natural sources)
- through supplements (although it comes in different forms and researchers aren't always consistent in their advice about which form is best)
- through sunshine or the ultraviolet rays from the sun to be more precise (but SPF 8 or greater, heavy cloud cover, skin color, aging, and even the angle of the sun in winter blocks vitamin D from being made in sufficient amounts)
So what is an over-50 year old adult to do?
First, choose foods that contain vitamin D or foods that are fortified with vitamin D: salmon, mackerel, tuna and sardines are good sources because fatty fish contain this fat-soluble vitamin. Mushrooms (they are being exposed to ultraviolet light to make them good sources), milk, some but not all yogurts (read the label), many breakfast cereals and orange juice contain vitamin D. A recent study found that half of vitamin D intake comes from milk so that is a good place to start.
Second, consider supplementation; you might be getting some in your multi-vitamin and most contain 400 IU (IU stands for international units, the measure used in supplements). Vitamin D comes in two forms--D2 and D3 and most, but not all, experts recommend the D3 form because early research showed that D3 is more effective at raising vitamin D blood levels than D2. However, some research shows that both forms are effective at improving blood levels.
Third, consider getting some sensible sun--10 to 15 minutes of sun exposure twice a week can improve vitamin D levels. This recommendations is controversial because UV rays from the sun or tanning beds are tied to the million of skin cancer diagnoses each year.
Which leads us back to that 40 ng/mL blood level--is that good or bad? According to the lab report 40 is a healthy level, but trending more toward the insufficient end of the range. A controversial article in an international osteoporosis journal suggests that older adults need 800 to 1000 IU of vitamin D each day to reach the maximal blood levels of vitamin D.
Next time you go to the doctor and have blood drawn, ask for a vitamin D level--in the meantime, increase your intake of vitamin D from foods and if you supplement, look at the supplement label to determine how much vitamin D your supplement provides.
For more information check out Dr. Michael Holick's website http://www.vitamindhealth.org/ or his new book, The Vitamin D Solution.