You can be the poster gal of healthy eating and take a multivitamin every morning, but thanks to the “usual suspects,” you can still come up short on nutrients your body needs.
And after 40, things like hormonal shifts can change how your body uses certain nutrients. Chronic stress can increase demand. Gut problems can interfere with absorption. Medications can quietly deplete nutrients over time. And if you’re eating less in an attempt to lose weight—or taking a medication that dramatically reduces your appetite—you may simply not be getting enough in the first place.
Unfortunately, nutrient deficiencies don't always announce themselves with an obvious symptom. You may feel tired. Foggy. Weak. Moody. Your hair starts thinning. Your sleep gets worse. Your muscles ache. Your workouts suddenly feel harder. Yet all your routine labs come back “in range.”
Here are 5 of the most common nutrient deficiencies I encountered when working with my patients—and why they’re particularly worth paying attention to after 40.
1. Folate
Folate is another deficiency I encountered fairly often in my patients, particularly in women with poor dietary intake, GI problems, excessive alcohol use, certain medications, or genetic variants that affect how the body processes folate.
I typically check folate along with vitamin B12 since the two nutrients work closely together. That's particularly important because supplementing folate can correct the anemia caused by B12 deficiency while potentially allowing the neurological complications of B12 deficiency to go unnoticed. I’ve seen it happen.
When supplementation is needed, I generally prefer methylfolate rather than synthetic folic acid, especially in patients with certain MTHFR variants. The dose depends on the degree of deficiency and what may be causing it in the first place. But when clinically indicated, many of my patients did well with doses ranging from 1,000 to 5,000 mcg per day.
2. Iron
Diagnosing iron deficiency can be tricky—especially if your practitioner is only checking your CBC or iron levels. In women over 40 who are still menstruating, one of the most common causes is blood loss from heavy menstrual periods. But in others—especially women who are no longer having menstrual cycles—other causes need to be evaluated, like certain prescription drugs, lack of stomach acid, poor absorption, or GI blood loss. Bottom line: iron deficiency rarely shows up simply because you aren't eating enough iron.
The blood test that is often the earliest indicator there’s an issue is ferritin. This is the storage form of iron, and levels can start dropping long before your CBC shows anemia. In my patients, I like to see the ferritin level above 50 ng/mL. I also do a more complete iron panel to get a clearer picture of how the body is handling iron storage and circulation.
My preferred form of oral iron is iron bisglycinate. It tends to be better tolerated than other forms. The dose depends on the level of deficiency, and I recheck levels 8 weeks after starting supplementation and at regular intervals thereafter as long as my patient remains on supplementation.
3. Magnesium
Magnesium is another nutrient that frequently comes up short, especially since stress, certain medications, GI problems, and inadequate dietary intake can all contribute to low levels. And because magnesium is involved in hundreds of reactions throughout the body, a deficiency can show up in all sorts of ways—including muscle cramps, headaches, constipation, poor sleep, fatigue, and even heart palpitations.
Unfortunately, testing magnesium isn't always straightforward. Most of the body's magnesium is stored inside cells and bone, so a normal serum magnesium level doesn't necessarily tell you the whole story. When I suspect a deficiency, I prefer to check a red blood cell (RBC) magnesium level, which I find more useful than serum magnesium alone.
And if you're going to supplement, the form matters. Magnesium glycinate is one of my favorites because it's well absorbed and tends to be easy on the GI tract. If constipation is also an issue, magnesium citrate may be a better choice since it can help get things moving. As with the other nutrients we've discussed, the dose depends on the person, the reason you're taking it, and how your body responds.
4. Vitamin D
Vitamin D is probably one of the best-known nutrient deficiencies—unless you live in Hawaii or get adequate sun exposure year-round. And a deficiency in this vitamin can pack quite a punch—since this nutrient plays an important role in bone health, muscle function, immune regulation, and many other processes throughout the body. That's particularly important for women after 40, when declining estrogen eventually accelerates bone loss.
When testing, most laboratories report a normal reference range of around 30 to 100 ng/mL. But for optimal health, I like to see it between 60 and 80 ng/mL. If my patients are particularly low, I may give them higher doses for the first few weeks, then cut back to a lower maintenance dose and retest 8 weeks later. I find that daily dosing with a pharmaceutical-grade vitamin D3 supplement works better than the prescription weekly form.
But keep in mind that vitamin D is a fat-soluble vitamin—which means it can accumulate in your body if you take too much. Excessive levels can lead to problems with calcium metabolism and even kidney stones. That’s why I routinely recommend testing vitamin D levels in patients who are supplementing with vitamin D.
5. Vitamin B12
Deficiencies in vitamin B12 are also quite common, especially in women who take acid-suppressing medications, have certain GI conditions, have had GI surgeries, have an autoimmune condition known as pernicious anemia, or eat little or no animal protein. Even age alone can deplete B12 levels—since normal stomach acid production declines over time, and stomach acid is required to release B12 from food so it can be absorbed.
The best form, route, and dose depend on why you're deficient. Someone with mildly inadequate dietary intake is a very different situation from someone who has undergone gastric bypass surgery and isn't absorbing nutrients normally.
Chapter 9 of my upcoming third book spends a lot of time on matching the right form of a nutrient to the person who actually needs it. But in general, many of my patients did well with an oral or sublingual dose of methylcobalamin, from 1,000 to 5,000 mcg daily.
As far as testing, there is abundant research showing that routine serum B12 testing can miss a functional B12 deficiency. That’s why I prefer to also test methylmalonic acid (MMA). It’s an indirect but more sensitive way to assess for true B12 deficiency, although kidney function also needs to be taken into consideration when interpreting the results.
I’ve seen way too many patients who’ve been told to stop their B12 supplements simply because their serum B12 levels were high. But if you’re taking B12, seeing an elevated B12 level on your blood work shouldn't exactly come as a surprise. That number alone doesn't tell you whether the B12 is actually doing its job at the cellular level.
Another important point: vitamin B12 is water-soluble, so your body can generally eliminate what it doesn’t need through your urine. That’s another reason an elevated B12 level in someone taking a supplement doesn’t automatically mean they’re getting too much or need to stop taking it.
Wrong test, wrong recommendation.
The Bottom Line
Nutrient deficiencies are among the most common—and overlooked—health issues I encountered in women over 40. That’s why I devote an entire chapter in all three books in my Weight Loss After 40 series to this topic.
Make a list of your symptoms and share them with your practitioner. If your routine labs come back stamped “normal,” ask them to dig deeper into possible nutrient deficiencies using the correct lab tests—especially if you have certain medical conditions that put you at higher risk.
And here’s an important parting point: supplement quality matters. Supplements vary considerably in their purity, potency, and manufacturing standards. While some products are carefully formulated, rigorously tested, and deliver what the label promises, others contain poorly absorbed nutrient forms, excessive fillers, or ingredient amounts that differ from what’s listed on the label.
I generally don’t recommend that my patients purchase supplements I use therapeutically from conventional drugstores, mass-market retailers, online third-party sellers, or franchise vitamin shops. While you can find some quality products there, there are far more inexpensive options that use different nutrient forms, doses, or formulations—or simply don’t meet the quality standards I’m looking for. When correcting nutrient deficiencies, I want to know exactly what my patients are getting—and that it’s the form and dose I intended.
You can find pharmaceutical grade supplements I recommend for my patients HERE.