Twin studies boost “sunshine-and-seafood” vitamin's preventive-health profile; adolescents in the northeast lack D and darker skin worsens situation
by Craig Weatherby
Recent days brought a minor deluge of vitamin D research over our transom. Here are three highlights, in brief:
Vitamin D-calcium combo may prevent and alleviate diabetes
More than 20 million Americans—nearly one in 10 adults—have diabetes. It cost the nation some $132 billion in 2002, according to the American Diabetes Association.
A new review of the evidence suggest that any of three dietary components—vitamin D, calcium, and dairy products— may reduce the risk of developing diabetes or decrease the severity of the disease.
Researchers from the Tufts-New England Medical Center in Boston examined evidence from epidemiological studies and from clinical trials in which participants took vitamin D and/or calcium supplements, with these results (Pittas AG et al 2007):
Evidence from clinical trials suggests that combined vitamin D and calcium supplementation may be especially helpful in preventing type-2 diabetes among people with glucose intolerance: an increasingly metabolic condition that usually precedes and probably helps cause diabetes.
Evidence from epidemiological studies showed a pretty consistent link between higher intakes of calcium or vitamin D or dairy foods (made from D-fortified milk) and lower risk of type-2 diabetes.
People with the highest intakes of any of these dietary factors had a 64 percent reduced risk of the disease.
Excluding people of African descent, those with the highest intakes of calcium or vitamin D or dairy foods had a 29 percent lower risk of metabolic syndrome (MetS or syndrome x): a cluster of signs, including glucose intolerance, that often precedes heart disease and diabetes.
Metabolic syndrome is defined as having three or more of a half-dozen metabolic risk factors:
- Abdominal obesity (excessive fat tissue in and around the abdomen).
- High blood triglycerides, low HDL cholesterol and high LDL cholesterol: a state that fosters plaque buildups in artery walls.
- Elevated blood pressure.
- Insulin resistance or glucose intolerance (the body can't properly use insulin or blood sugar).
- Pro-thrombotic state that promotes dangerous clots (e.g., high fibrinogen or plasminogen activator inhibitor-1 in the blood).
- Pro-inflammatory state (e.g., elevated C-reactive protein in the blood).
Low vitamin D levels may raise metabolic syndrome risk
Results of a study from Madrid, Spain indicate that obese people with low blood levels of vitamin D run a greater risk of developing metabolic syndrome (MetS).
According to the American Heart Association, more than 50 million Americans—nearly one in four adults—have MetS, which raises the risk of developing cardiovascular disease, stroke, and type 2 diabetes.
The research adds to a fast-building body of data linking vitamin D deficiency to increased risk of type-2 diabetes, osteoporosis, and certain cancers.
As the Spaniards wrote, ”…patients with and without vitamin D deficiency had similar BMI and waist circumference, so the differences in metabolic syndrome prevalence and lipid levels may indeed reflect a true association between vitamin D status and the metabolic syndrome…” (Botella-Carretero JI et al 2007).
More than 60 percent of those with MetS were vitamin D deficient, compared to only 33 per cent of those without the syndrome.
In addition, the vitamin D-deficient participants had undesirable blood profiles, with lower blood levels of HDL-cholesterol and higher levels of triglycerides, compared to those with adequate vitamin D levels.
The term “vitamin D” encompasses two forms. Vitamin D3, which is the most effective form, is found primarily in fish and a few other animal foods, and is produced in skin exposed to UV sunrays,. Vitamin D2 is the weaker form, derived from plants and used in most vitamin supplements.
Kids in northern climes at risk of low vitamin D levels
It's been known for decades that vitamin D levels correlate pretty closely with latitude, sine the vitamin is produced by exposure to UV sunrays. For example, a 2006 study from Britain—a cloudy, northern nation—found that over 70 percent of teenage girls were vitamin D deficient.
People with dark skin—which blocks some of UV sunrays and thereby reduces production of vitamin D—are even worse off.
Now, doctors at The Children's Hospital of Philadelphia report finding that about 55 percent of adolescents in the northeastern US—and most likely kids in other northerly states—are vitamin D deficient: a status that puts them at increased risk of osteoporosis, heart disease, cancer, and possibly other health problems in adulthood (Weng FL et al 2007).
Worse, more than one in 10 African-American adolescents were found deficient in vitamin D.
The deficiencies were also worse in the winter and among older teens and those with low vitamin D intakes from food and supplements.
The authors noted that the recommended intake levels for dietary vitamin D (400 IU per day) are probably too low to maintain healthy levels among kids in relatively un-sunny northern latitudes, and especially darker skinned teens.
They suggest fortifying foods other than milk, since many children do not enough to meet their calcium or vitamin D needs. And drinking ten glasses of milk a day—the amount required to meet current intake advice from experts in the field (1,000 IU per day)—would be a nutritionally knuckle-headed approach anyway.
Supplements and fatty fish are both much higher in vitamin D than milk, and fish such as wild Sockeye Salmon (687 IU per 3.5 oz serving) offer the benefits of very high protein and omega-3 content as well.
- Pittas AG, Lau J, Hu FB, Dawson-Hughes B. The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis. J Clin Endocrinol Metab. 2007 Jun;92(6):2017-29. Epub 2007 Mar 27. Review.
- Botella-Carretero JI, Alvarez-Blasco F, Villafruela JJ, Balsa JA, Vazquez C, Escobar-Morreale HF. Vitamin D deficiency is associated with the metabolic syndrome in morbid obesity. Clin Nutr. 2007 Jul 9; [Epub ahead of print]
- Weng FL, Shults J, Leonard MB, Stallings VA, Zemel BS. Risk factors for low serum 25-hydroxyvitamin D concentrations in otherwise healthy children and adolescents. Am J Clin Nutr. 2007 Jul;86(1):150-8.