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Selecting the Best Vitamin D Supplement: Our Criteria


How do you know which Vitamin D supplement is the best one? What’s the best form of Vitamin D? What about dosage? With so many to choose from, if you are wondering how to choose the best Vitamin D supplement, we can offer a tip or two; we just developed our own, with scientific input from one of the foremost researchers of Vitamin D in the United States. Today, we share how we developed our Vitamin D criteria and show you our non-negotiables. Let’s dive in.


Why Vitamin D?

Vitamin D is an essential vitamin that supports bone health in the preconception period, during pregnancy and while nursing. As a supplement, Vitamin D is increasingly used at fertility centers worldwide to support reproductive health in both men and women. We also know that Vitamin D may have other helpful functions, such as supporting a healthy immune system and supporting normal mental function and nerve growth. 

Naturally, we wanted Vitamin D to be the next supplement to augment our growing line of reproductive and prenatal health supplements to support the journey of our community.


Varying Vitamin D Recommendations

Doctors and scientists generally agree that Vitamin D is an essential vitamin that supports the health of the mom and baby. However, there is a surprising amount of debate among experts when it comes to just how much Vitamin D our bodies need daily to maintain health and how much Vitamin D should be circulating in our body.

The Institute of Medicine’s latest guidelines from 2010 state that 20 ng/mL of Vitamin D (specifically, 25-hydroxy-vitamin D) in the blood is sufficient, while the Endocrine Society’s 2011 guidelines recommend 30-60 ng/mL. Some experts recommend even higher levels, while others say a much lower levels at 12.5 ng/mL are sufficient. Correspondingly, recommendations for daily intake vary widely. Quickly, it became clear we needed solid, science-driven guidance.

In Bruce Hollis, PhD, we found that expert.


Dr. Bruce Hollis, the Vitamin D Expert

Our Vitamin D Advisor - Dr. Bruce Hollis

Dr. Hollis, a lifelong researcher of Vitamin D, is a Professor of Pediatrics at Medical University of South Carolina. His laboratory was the first to develop a Vitamin D assay, approved by the FDA for clinical diagnostics. Dr. Hollis has used these Vitamin D assays to understand how Vitamin D works in the human body, including in calcium homeostasis, pregnancy and lactation.

Throughout the year-long process that started in 2020 in the midst of the COVID-19 pandemic, Dr. Hollis guided us on the development process, formulation and dosage based on the most up-to-date understanding of Vitamin D.


Criteria for a Good Vitamin D Supplement

With Dr. Hollis’ scientific input, we outlined our Vitamin D criteria. This is the criteria we followed to develop our Vitamin D3+K2 supplement, but we think it’s a good rule of thumb for anyone looking for a high-quality Vitamin D supplement.


  • Vitamin D3 form: There are two major forms of Vitamin D. One (Vitamin D2) is found in plants, and the other (Vitamin D3) is the form of Vitamin D that our skin synthesizes when exposed to UVB – and is the more natural form to the human body.
  • Vegan Vitamin D3: Many Vitamin D3 supplements on the market use Vitamin D3 sourced from animals, making it unsuitable for vegans and strict vegetarians. (Lanolin from sheep and fish oil are the two common sources.) Because vegans and vegetarians are at higher risk of not getting enough Vitamin D from their diet, we feel it’s important to source vegan-friendly Vitamin D3 from lichen.
  • Addition of Vitamin K2 in the MK-7 form: Vitamin K2 works together with Vitamin D to regulate calcium and phosphorus levels, which helps maintain bone health. To take advantage of this synergy between the two vitamins, a Vitamin D supplement should contain Vitamin K2 in the menaquinone-7 (MK-7) form.
  • Liquid formula: If you are the kind of person who does everything in your power to support your reproductive health or health in general, you are probably already taking more than a few tablets and capsules every day. (Ask us why we know!) A liquid Vitamin D formula is attractive from that perspective, rather than adding one more capsule to your daily routine.
  • Natural lemon flavor: Natural and relatively neutral lemon flavor makes it easy to add a drop or two of Vitamin D to your morning smoothies, a bowl of yogurt or even to your salad dressing.
  • Organic olive oil: Both Vitamin D3 and Vitamin K2 are fat-soluble vitamins, and are better absorbed when ingested with fat. In a reproductive and prenatal health supplement, organic olive oil is a more suitable carrier oil than the typical synthetic oil, such as MCT.
  • High-concentration with an easy-dosing dropper: Doctors’ recommendation on Vitamin D supplementation dosage vary widely, depending on your needs and Vitamin D levels. (And yes, depending on which guideline each doctor follows, too.) A high-concentration Vitamin D with each drop containing 1,000 IU makes it easy to follow your doctor’s specific recommendation, which usually comes in multiples of 1,000 IU per day. Many liquid Vitamin D supplements fall short of this concentration – that can mean a tedious daily counting of many drops to get the amount you need.



Of course, there are other general non-negotiable for us, such as a GMP certification of the manufacturing facility, strict quality assurance process and trust by fertility experts, but we hope our Vitamin D-specific criteria was helpful. 

If you have any questions, feel free to reach out to us via LiveChat. We are with you.




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