New light on sunshine vitamin
Regarding the article “The power of D” (SN: 7/16/11, p. 22), I was very surprised that there was no mention of the positive effects of this vitamin on the debilitating effects of depression. I have lived in northern latitudes between upstate New York and now Vermont since my birth in 1954. My mother reminds me how she used to worry about the annual return of my severe depression as a young child, which turned more serious in January. I have childhood memories of colds, bronchitis and pneumonia.

However, after attending a lecture in Lenox, Mass., two years ago on the subject of vitamin D, I have been taking larger doses of vitamin D and my depression has virtually disappeared.

When my doctor learned that I was doing this, he shared his concern about potential toxicity. But tests showed my blood levels for vitamin D were normal. I would imagine that everyone has to define the exact amounts right for their body for themselves, but I do know that this little golden and translucent pill has saved my life.
Liz Winn, Marshfield, Vt.

Many studies have linked vitamin D deficiency with depression. A German study in 2000 found that people with depression had lower levels of vitamin D than those without the condition, and in 1999 a U.S. study showed that a megadose of vitamin D (100,000 IU) resulted in improvement in depression scores in people with seasonal affective disorder. A third study in Norway in 2008 randomly assigned depressed, overweight people to get vitamin D supplements or placebos for a year without knowing which. Those receiving vitamin D showed substantial improvement; those on placebo did not. — Nathan Seppa

In your five-page article on vitamin D, you report that 30 minutes of exposure to sunlight provides about 10 times the upper recommended daily allowance (2,000 international units or IU recommended by the Endocrine Society) of the vitamin, yet devote much of the discussion of the appropriate level of vitamin D to far less effective means (natural and fortified food, and pharmaceuticals). Wouldn’t recommending that everybody take each day a five-minute tan (free, less time-consuming than other means of obtaining vitamin D, and certainly not sufficient to get a sunburn) render this whole matter moot?
Ernst L. Leiss, via e-mail

In order to neither underdose nor overdose on vitamin D, it seems to make sense to measure vitamin D blood levels before deciding on how much to supplement.
Stan Rosenfeld, Fairfax, Calif.

In “The power of D,” two additional aspects should have been included. First, it is ultraviolet B sunlight, the burning wavelength region, which is necessary to create vitamin D in our skin. During the winter, even in southern regions of the United States, it may be difficult to get enough exposure to ultraviolet B from the sun.

Second, you did not deeply discuss concerns about exposure to high, possibly toxic levels of vitamin D supplements. I believe this issue involves possible kidney damage, but I am not aware of the evidence behind these concerns. Such a discussion would have further enriched your excellent review.
James P. Collman, via e-mail

Overdosing on vitamin D from the sun appears impossible. The body has a fail-safe mechanism that shuts down the vitamin D–making apparatus in the skin when levels are topped up. Supplements are another matter, but it still takes a lot to overdose on vitamin D. Danish researchers in 1986 found that people taking 4,000 IU of vitamin D daily for two months ended up with blood levels of about 45 nanograms per milliliter, well within the normal range and somewhat less than an outdoor lifeguard would have all summer. Reinhold Vieth of the University of Toronto finds that his and other studies arrive at 10,000 IU a day as a safe upper daily limit.

The Institute of Medicine in 2010 set the safe upper limit of vitamin D per day for an adult at 4,000 IU. The Endocrine Society in 2011 put the daily limit for adults at risk for vitamin D deficiency at 10,000 IU. The 10,000 IU mark falls within evolutionary bounds by not exceeding what full-body exposure to sun delivers in a day. — Nathan Seppa

IQ droppers
According to “Chemicals linked to kids’ lower IQs” (SN: 5/21/11, p. 15), neurotoxic chemicals may lower children’s IQs by up to 7 points. There is another substance associated with a similar IQ point difference in children, but no one mentions it. The point spread between breast-fed and formula-fed children has been that large in some studies.

Parents are told about the IQ drop of up to 7 points with pesticides. They’re told about the IQ drop with low-level lead exposure. Don’t they deserve to know about the population-wide IQ deficit linked to formula-feeding? Maybe if they knew, they’d insist on more than the mediocre breast-feeding help with which most women are forced to make do.
Diane Wiessinger, Ithaca, N.Y.

I am a retired chemical engineer who has had a subscription to Science News magazine for a couple of years. It excels in covering many science disciplines concisely, understandably and timely. Because it is valuable to my continuing interest in science, I look forward to receiving each issue.
William Scudder, Sarasota, Fla.