Correlating A1C To Average Blood Glucose (And Vice Versa)

It might be easier to understand a hemoglobin A1C (HbA1C or just A1C) reading if it was given in the same units as blood sugar. There are calculators that can correlate your A1C to an average blood glucose value, or, as the American Diabetes Association (ADA) calls it, an "estimated average glucose" or eAG.

Here's the ADA's calculator. (The image should take you to their site.)



The ADA gives the relationship between A1C and eAG as: 28.7 x A1C – 46.7 = eAG.

Which works out to:



While I'm at it, here's ACCU-Chek's calculator. (The image should take you to their site.)



ACCU-Chek's caveat is important:

"This tool uses average plasma blood sugar readings — the measure used by most meters available today. It should not be used to predict an A1C and is not a substitute for a clinical test performed by your doctor. It is intended to show the relationship between a healthy A1C and self-monitoring results, and give you an idea of how you can help prevent long-term diabetes complications."

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CDC Diabetes Fact Sheet

This is a great fact sheet on diabetes from the Centers for Disease Control (CDC). It would be handy for anyone doing a school project or giving a presentation. At 12 pages, it's more of a brochure than a sheet:


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Is High Blood Pressure In The Elderly Not As Risky?

The risks associated with hypertension, high blood pressure (BP) as it's commonly called, may be different for very old compared to younger adults. Paula Span, who writes the New Old Age Blog at the New York Times discussed this in her post:

For the Very Old, a Surprise in Blood Pressure Readings, New York Times, 8 August 2012

Span writes:

"I was startled to learn that in the very elderly - those over 85, say - high blood pressure may indicate better health while lower numbers could mean trouble ahead."

Span had been reading a study and an accompanying editorial published in the Archives of Internal Medicine last year:

Rethinking the Association of High Blood Pressure With Mortality in Elderly Adults, JAMA Internal Medicine, August 2012
Comment on “Rethinking the Association of High Blood Pressure With Mortality in Elderly Adults," Goodwin JS, JAMA Internal Medicine, August 2012

In his editorial, Goodwin offered some background:

"In 1988, Matilla et al reported that, among the very old, elevated systolic and diastolic blood pressure (BP) were associated with longer survival. The differences were not subtle. The 5-year survival of those with systolic BPs greater than 200 mm Hg were almost twice as high as those with levels of 120 to 140 mm Hg. Over the ensuing 25 years, a substantial number of population-based studies have reported the same findings: in those older than 85 years (or older than 80 years in some studies), high BP is an excellent prognostic sign.

Perhaps the most rigorous assessment came from the Framingham Study, which reported that the strong positive association of BP with cardiovascular mortality was reversed between the ages of 75 and 85. Importantly, no population-based study has found the opposite, that high BP is a marker for bad outcomes in octogenarians. Conversely, “normal” BP is bad. Perhaps the worst sign is falling BP."

Why does high BP appear to be a good sign in an older population? Goodwin explains that the old are a mixture of frail and more robust individuals.  High BP does not connote the same level of health in both groups.  Referring to Diehr et al. he said:

"[The very old] showed a steady decrease in BP in the 3 years before death. ... High BP is only a good sign in very old age because many of those with “normal” BP have it for bad reasons."

When is it advantageous to treat high blood pressure in an older person? Goodwin says:

"Many robust, very old individuals have hypertension. Antihypertensive treatment in those individuals is beneficial. Frail older individuals are less likely to have hypertension, and treating those who do may produce bad outcomes."

How do you measure robustness? One good test is walking speed.

In the study at the top of this post, those with hypertension who could walk a 20-foot corridor at an average pace of 1.8 mph or better had about the same risk of dying as younger adults. Those with high BP who walked slower did not have an increased risk. And those with high BP who couldn't complete the walk had a 60% lower risk of death:

"Higher systolic BP was associated with an increased risk of mortality only among elderly adults who had a medium to fast walking pace. In contrast, among slower-walking older adults, there was not an association between elevated systolic or diastolic BP and mortality. Strikingly, we found elevated systolic and diastolic BP was strongly and independently associated with a lower mortality risk in participants who did not complete the walk test."

The lead author of the study, Dr. Michelle Odden, said:

"The paradigm in medicine is, high blood pressure is bad, treating it is good. We’re saying, maybe we need to look more closely at the guidelines and tailor them more to older adults."

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Dietary Fat Increases Blood Glucose and Insulin Requirements

It isn't just carbohydrates people with diabetes need to be vigilant about. It's the fat too.

A new study from the Joslin Clinic in Boston found that patients with type 1 diabetes required more insulin coverage for a higher-fat meal compared to a lower-fat meal. The meals were prepared in the Clinic's kitchen and had identical carbohydrate and protein, but different fat content - 60 grams vs. 10 grams. The carbohydrates in the meals had similar glycemic indexes.

Dietary Fat Acutely Increases Glucose Concentrations and Insulin Requirements in Patients With Type 1 Diabetes, Diabetes Care, April 2013

It was a small study of crossover design, meaning each participant consumed both the high-fat meal and the low-fat meal.

"RESULTS Seven patients with type 1 diabetes (age, 55 ± 12 years; A1C 7.2 ± 0.8%) successfully completed the protocol. [The high-fat] dinner required more insulin than [the low-fat] dinner (12.6 ± 1.9 units vs. 9.0 ± 1.3 units; P = 0.01) and, despite the additional insulin, caused more hyperglycemia.

CONCLUSIONS This evidence that dietary fat increases glucose levels and insulin requirements highlights the limitations of the current carbohydrate-based approach to bolus dose calculation. These findings point to the need for alternative insulin dosing algorithms for higher-fat meals and suggest that dietary fat intake is an important nutritional consideration for glycemic control in individuals with type 1 diabetes."

Joslin accompanied their study with this short video:

"When people ate a higher fat meal, their blood sugars were higher for longer and required more insulin."

Why does dietary fat lead to higher blood glucose? It is thought that fat contributes to insulin resistance:

"Dietary fat and free fatty acids (FFAs) are known to impair insulin sensitivity and to enhance hepatic glucose production. ... Interventions that lower [free fatty acid] levels in nondiabetic and type 2 diabetic individuals lead to both improved insulin sensitivity and glucose tolerance."

Saturated fat may be more problematic:

"Studies in nondiabetic individuals indicate that saturated fats cause more profound insulin resistance than monounsaturated and polyunsaturated fats. By design, the [high-fat] dinner meal in the current study was predominantly saturated fat."

And:

"Pizza is widely recognized to cause marked late postprandial hyperglycemia in patients with type 1 diabetes."

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You Don't Have To Be Taking Metformin Or Have Diabetes To Risk Vitamin B12 Deficiency

Before I leave the topic of vitamin B12 (yesterday's post: New Study Links Metformin To Cognitive Impairment, via inadequate vitamin B12), it's important to know that you don't have to be taking metformin, or have diabetes at all, to risk a vitamin B12 deficiency.

The National Institutes of Health (NIH) say between 1.5% and 15% of the US population experience vitamin B12 deficiency. Most people over the age of 50 have such poor absorption of the vitamin that the NIH recommends older adults supplement with B12, either by eating fortified foods or taking dietary supplements.

From the NIH Office of Dietary Supplements:
Quick Fact Sheet on Vitamin B12
Professional Fact Sheet on Vitamin B12

Groups that may not be getting enough vitamin B12 or that have trouble absorbing it:

• Many older adults, who do not have enough hydrochloric acid in their stomach to absorb the vitamin B12 naturally present in food. People over 50 should get most of their vitamin B12 from fortified foods or dietary supplements because, in most cases, their bodies can absorb vitamin B12 from these sources.
• People with pernicious anemia whose bodies do not make the intrinsic factor needed to absorb vitamin B12. Doctors usually treat pernicious anemia with vitamin B12 shots, although very high oral doses of vitamin B12 might also be effective.
• People who have had gastrointestinal surgery, such as weight loss surgery, or who have digestive disorders, such as celiac disease or Crohn's disease. These conditions can decrease the amount of vitamin B12 that the body can absorb.
• Some people who eat little or no animal foods such as vegetarians and vegans. Only animal foods have vitamin B12 naturally. When pregnant women and women who breastfeed their babies are strict vegetarians or vegans, their babies might also not get enough vitamin B12.

Low levels of vitamin B12 show up as numbness or tingling in the arms and legs, weakness, and loss of balance - symptoms similar to diabetic neuropathy. Other symptoms include constipation, loss of appetite, weight loss, soreness of the mouth or tongue, and megaloblastic anemia. And as we saw in yesterday's post, vitamin B12 deficiency affects cognition, leading to depression, confusion, poor memory, and dementia.

A vitamin B12 deficiency can be detected by a blood test. Also, an elevated mean corpuscular volume (MCV) in a blood test can indicate low B12 status and justifies measurement of serum B12 directly.¹
________ ¹ Diagnostic Value Of The Mean Corpuscular Volume In The Detection Of Vitamin B12 Deficiency, Scandivavian Journal of Clinical and Laboratory Investigation, February 2000.

New Study Links Metformin To Cognitive Impairment

A new study from Australia finds that people with diabetes who take metformin suffer more cognitive problems than those who don't take the drug:

Increased Risk Of Cognitive Impairment In Patients With Diabetes Is Associated With Metformin, Diabetes Care, October 2013

"Participants with diabetes had worse cognitive performance than participants who did not have diabetes. ... Among participants with diabetes, worse cognitive performance was associated with metformin use."

Why does metformin affect cognitive performance? It's thought that the drug interferes with the absorption of vitamin B12, by interacting with a B12 receptor in the distal ileum, and B12 is necessary for a well-functioning nervous system. Indeed, in this study vitamin B12 and calcium supplementation was associated with better cognition.

Dr. Adriaan Kooy from the Bethesda Diabetes Research Center in the Netherlands says:

"The malabsorption of neurovitamins like B12 in metformin users may contribute to neuronal dysfunction — potentially being misinterpreted as diabetic neuropathy."

The link between metformin and vitamin B12 isn't new, but the affect on mental function is becoming more apparent. The study's lead author, Eileen Moore, PhD, told Medscape Medical News:

"Since the 1970s, clinicians and scientists have been aware that metformin is associated with lower vitamin-B12 levels. The hypothesis that this may increase the risk of cognitive impairment seemed sound."

Moore advises:

"Vitamin-B12 levels in patients using metformin should be monitored at least yearly."

Dr. Kooy's group published evidence of the link between metformin and vitamin-B12 deficiency a few years ago:

Long Term Treatment With Metformin In Patients With Type 2 Diabetes And Risk Of Vitamin B-12 Deficiency: Randomised Placebo Controlled Trial, British Medical Journal, May 2010

They had the same advice:

"Long term treatment with metformin increases the risk of vitamin B-12 deficiency, which results in raised homocysteine concentrations. Vitamin B-12 deficiency is preventable; therefore, our findings suggest that regular measurement of vitamin B-12 concentrations during long term metformin treatment should be strongly considered."

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