Sadly, sloppy headlines may mislead people into undue skepticism about the value of targeted nutrition for disease prevention.
Media coverage of a report from the U.S. Preventive Services Task Force (USPSTF) – a U.S. government advisory panel – is a case in point.
The USPSTF panel reviewed the available evidence and concluded that supplements of high-dose calcium plus low-dose vitamin D don’t reduce the risk of bone fractures among postmenopausal women.
But the panel was careful to note that more evidence is needed in order to determine whether higher doses – especially higher doses of vitamin D – would help.
(The vitamin D dose in most “bone supplements” (400 IU) – which is the dose used in most studies – falls well short of the new RDA (600 IU) set in late 2010, which is deemed inadequate by many leading researchers … see “Vitamin D RDAs Raised Substantially”.)
And the USPSTF panel decided there’s ample evidence that vitamin D can help prevent falls in people aged 65 or older, who inherently are at increased risk for falling.
Yet, most of the headlines we’ve seen don’t convey the distinctions drawn by the panel … a flaw common to many media stories about nutrition and supplements.
The panel also advised women to have a bone density scan at age 65 … or a decade earlier if they have risk factors for osteoporosis, such as celiac disease, a family history of osteoporosis or premature menopause.
Advisory panel notes lack of evidence on higher doses
One in two postmenopausal women suffer a bone fracture … and this is no minor concern for older women (e.g., over 65 years old), as they can lead to much bigger problems.
The USPSTF’s main conclusion is that – with regard to postmenopausal women – “… there is adequate evidence that daily supplementation with 400 IU of vitamin D3 combined with 1,000 mg of calcium carbonate has no effect on the incidence of osteoporotic fractures.”
(Calcium carbonate, the cheapest and most common supplemental form, is also the least well-absorbed and the one most likely to cause kidney stones. However, there’s no good evidence that better-absorbed forms like calcium citrate are superior bone-protectors … see “High-dose calcium raises minor kidney stone risk”, below.)
But the panel stressed that we need more studies to find out whether higher doses would be more effective:
“The USPSTF concludes that the current evidence is insufficient to assess the balance of the benefits and harms of daily supplementation with more than 400 IU of vitamin D3 and 1,000 mg of calcium for the primary prevention of fractures in non-institutionalized postmenopausal women.”
That statement underscores the fact that – contrary to popular belief – evidence on the ability of supplemental nutrients to prevent diseases is hard to come by.
Omega-3s are one exception, as they have been more extensively studied than most nutrients, and enjoy broad support from world health authorities.
Often, the vast majority of evidence on nutrients and health comes from epidemiological studies, which cannot prove a cause-and-effect relationship.
And the few clinical trials funded by the government or foundations often use low doses, or blends of nutrients …flaws that render the outcomes muddy or meaningless.
High-dose calcium raises minor kidney stone risk
The panel also cited “adequate” evidence of a minor risk of kidney stones from taking these combined doses of D3 and calcium:
“… supplementation with 400 IU of vitamin D3 and 1,000 mg of calcium carbonate [or more] increases the incidence of renal stones. The USPSTF assessed the magnitude of this harm as small.”
Most calcium supplements include vitamin D, and the “seafood-and-sunshine” nutrient shouldn’t take unfair blame for a risk that almost certainly belongs to the high-dose calcium part of that very common combination.
The available evidence clearly indicates that high-dose calcium (i.e., 1,000 to 2,00mg per day) – rather than high-dose vitamin D3 (i.e., 1,000 to 4,000 IU per day) – raises the risk of kidney stones.
A daily dose of 1000mg of supplemental calcium is a very high intake, relative to countries where total dietary calcium intakes are much lower and vitamin D blood levels are much higher than in America, yet fracture risk is much lower.
The U.S. Preventive Services Task Force (USPSTF). Vitamin D and Calcium Supplementation to Prevent Cancer and Osteoporotic Fractures in Adults: U.S. Preventive Services Task Force Recommendation Statement. Accessed at http://www.uspreventiveservicestaskforce.org/draftrec3.htm