Vitamin D works more like a hormone than a vitamin, helping the body to absorb calcium, and improving the mineral density of the bones. Research indicates that vitamin D (measured as 25-hydryoxy (OH) vitamin D) can also help prevent many chronic diseases, such as heart disease, colon and breast cancer, and diabetes, as well as bone disorders.
Studies reveal that up to 80 percent of people with severe obesity (body mass index of 40 or greater) have low vitamin D levels, possibly related to the fact that vitamin D is a fat-soluble vitamin and tends to hide out inside fat cells where it can't be easily accessed by the body.
Research also suggests that low vitamin D levels can suppress leptin, a protein hormone that plays a role in regulating appetite by helping the brain to sense the feeling of fullness. Therefore, low vitamin D levels could exacerbate weight gain by switching off the feeling of satiety after eating.
Vitamin D deficiency is rapidly being recognized as an emerging public health issue, not only because of its connection to obesity, but also because of its strong association with osteoporosis, especially in the elderly and in young adults. According to the National Osteoporosis Foundation, more than 60 million Americans, 41 million of whom are women, are likely to have either osteoporosis or low bone mass by the year 2020. People on cholesterol-lowering medications are also at risk for deficiency.
Children may be at risk: A study at Children's Hospital in Boston found approximately 62 percent of the children in its care had levels of vitamin D less than 30 ng/mL, what's now considered to be the minimum cut-off point for normal. People on cholesterol-lowering medications are also at risk for deficiency.
How much vitamin D is enough? The Institute of Medicine recommends 200 IUs/day of vitamin D for women 50 or younger, 400 IUs/day for both men and women ages 51 to 70 years, and 600 IUs/day for anyone over the age of 70. And recent research suggests that these levels will be increased.
Calcium is crucial. Calcium is a mineral that goes hand-in-hand with vitamin D, and at least 1,000 mgs per day are recommended (with higher doses for some individuals, such as those who have had weight-loss surgery), in divided doses of no more than 500 mgs at a time, for optimal absorption. The quality, as well as quantity of calcium is important. Calcium citrate is preferred over calcium carbonate, since the carbonate form requires a very acidic environment for best absorption, while citrate does not. Therefore, anyone on antacids or proton pump inhibitors (PPIs), or anyone with less than normal acid levels in their stomach can't absorb calcium carbonate as well as they can calcium citrate.
Sources of vitamin D. One of the biggest sources of vitamin D come from direct sunlight falling on one's skin. Even in a sunny climate, however, the sunscreen necessary to protect against skin cancer blocks out the rays that induce the skin to produce vitamin D. This means that vitamin D supplementation is most likely going to be necessary for most people. Dietary sources of vitamin D are limited and include fatty fish, fish oils, and fortified milk products—and you'd have to drink a whole quart of vitamin D-fortified milk to get 400 IUs of vitamin D, which is a lot of milk!
Bottom line: It's important to know your (25-hydroxy) vitamin D level. Also, check with your doctor and dietitian about your individual calcium and vitamin D needs, including possible supplementation.
